feat: uBlock Origin Lite integration for ad-blocking during WebPage captures

- singlefile.rs: when ARCHIVR_UBLOCK=true and ARCHIVR_UBLOCK_EXT is set,
  archivr owns Chrome's lifecycle (--headless=new, --remote-debugging-port,
  --load-extension); single-file connects via --browser-server instead of
  launching its own Chrome. Falls back to old behaviour with ublock_skipped=true
  when the ext path is missing or invalid.
- capture.rs: thread ublock_skipped through CaptureResult
- database.rs: add notes_json TEXT column to capture_jobs (DDL + idempotent
  ALTER TABLE migration); update_capture_job_status gains notes_json param
- archive.rs: expose notes_json in CaptureJobSummary
- routes.rs: store {"ublock_skipped":true} in notes_json on completed captures
- ToastStack.jsx: warning toast variant (toast--warning) with Details expander
  and Ignore button
- CaptureDialog.jsx: fire warning toast when poll result has ublock_skipped
- App.jsx: sessionStorage-backed Ignore suppression for ublock warnings
- styles.css: .toast--warning (amber left border) + .toast-warning-detail
- flake.nix: ublockLite derivation fetches uBOLite_2026.705.2152.chromium.zip
  (pinned SHA256) from uBlockOrigin/uBOL-home; sets ARCHIVR_UBLOCK_EXT in both
  archivr and archivr-server wrappers

Env vars:
  ARCHIVR_UBLOCK=true (default) — enable uBlock during WebPage captures
  ARCHIVR_UBLOCK_EXT — path to unpacked uBOL extension dir (set by Nix)

frontend/src/App.jsx

@@ -85,6 +85,9 @@ export default function App() {
 
   const [toasts, setToasts] = useState([])
   const toastIdRef = useRef(0)
+  const [ublockWarningIgnored, setUblockWarningIgnored] = useState(
+    () => sessionStorage.getItem('ublockWarningIgnored') === 'true'
+  )
 
   const humanizeTags = currentUser?.humanize_slugs ?? false;
 
@@ -238,15 +241,22 @@ export default function App() {
     ])
   }, [archiveId, searchQuery, tagFilter, loadEntries])
 
-  const handleToast = useCallback((errorText, locator) => {
+  const handleToast = useCallback((text, locator, type = 'error') => {
+    if (type === 'warning' && ublockWarningIgnored) return
     const id = ++toastIdRef.current
-    setToasts(prev => [...prev, { id, errorText, locator }])
-  }, [])
+    setToasts(prev => [...prev, { id, text, locator, type }])
+  }, [ublockWarningIgnored])
 
   const handleDismissToast = useCallback((id) => {
     setToasts(prev => prev.filter(t => t.id !== id))
   }, [])
 
+  const handleIgnoreUblock = useCallback(() => {
+    sessionStorage.setItem('ublockWarningIgnored', 'true')
+    setUblockWarningIgnored(true)
+    setToasts(prev => prev.filter(t => t.type !== 'warning'))
+  }, [])
+
   if (authState === 'loading') return <div className="auth-loading">Loading\u2026</div>;
   if (authState === 'setup')   return <SetupPage onComplete={() => setAuthState('login')} />;
   if (authState === 'login')   return <LoginPage onLogin={user => { setCurrentUser(user); setAuthState('authenticated'); }} />;
@@ -347,7 +357,7 @@ export default function App() {
           onCaptured={handleCaptured}
           onToast={handleToast}
         />
-        <ToastStack toasts={toasts} onDismiss={handleDismissToast} />
+        <ToastStack toasts={toasts} onDismiss={handleDismissToast} onIgnoreUblock={handleIgnoreUblock} />
       </>
     </AuthContext.Provider>
   )

frontend/src/components/CaptureDialog.jsx

@@ -186,6 +186,13 @@ export default function CaptureDialog({ open, archiveId, onClose, onCaptured, on
             })
           }, 1400)
           onCapturedRef.current()
+          // Warn if uBlock was requested but the extension wasn't available
+          try {
+            const notes = updated.notes_json ? JSON.parse(updated.notes_json) : null
+            if (notes?.ublock_skipped) {
+              onToastRef.current(null, locator, 'warning')
+            }
+          } catch {}
         } else if (updated.status === 'failed') {
           clearInterval(pollIntervals.current.get(jobUid))
           pollIntervals.current.delete(jobUid)

frontend/src/components/ToastStack.jsx

@@ -1,22 +1,23 @@
 import { useState, useEffect } from 'react'
 
-const TOAST_TTL = 7000 // ms before auto-dismiss; paused when error is expanded
+const TOAST_TTL = 7000 // ms before auto-dismiss; paused when detail is expanded
 
-export default function ToastStack({ toasts, onDismiss }) {
+export default function ToastStack({ toasts, onDismiss, onIgnoreUblock }) {
   if (!toasts.length) return null
   return (
     <div className="toast-stack" role="log" aria-live="polite" aria-label="Notifications">
       {toasts.map(t => (
-        <Toast key={t.id} toast={t} onDismiss={onDismiss} />
+        <Toast key={t.id} toast={t} onDismiss={onDismiss} onIgnoreUblock={onIgnoreUblock} />
       ))}
     </div>
   )
 }
 
-function Toast({ toast, onDismiss }) {
+function Toast({ toast, onDismiss, onIgnoreUblock }) {
   const [expanded, setExpanded] = useState(false)
+  const isWarning = toast.type === 'warning'
 
-  // Auto-dismiss after TTL; paused while error detail is expanded
+  // Auto-dismiss after TTL; paused while detail is expanded
   useEffect(() => {
     if (expanded) return
     const timer = setTimeout(() => onDismiss(toast.id), TOAST_TTL)
@@ -27,6 +28,50 @@ function Toast({ toast, onDismiss }) {
     ? (toast.locator.length > 48 ? toast.locator.slice(0, 45) + '\u2026' : toast.locator)
     : null
 
+  if (isWarning) {
+    return (
+      <div className="toast toast--warning" role="alert" aria-atomic="true">
+        <div className="toast-top">
+          <span className="toast-icon" aria-hidden="true">⚠</span>
+          <div className="toast-body">
+            <span className="toast-headline">Ad-blocking unavailable</span>
+            {short && <span className="toast-locator">{short}</span>}
+          </div>
+          <div className="toast-btns">
+            <button
+              type="button"
+              className="toast-view-btn"
+              onClick={() => setExpanded(v => !v)}
+              aria-expanded={expanded}
+            >
+              {expanded ? 'Hide' : 'Details'}
+            </button>
+            <button
+              type="button"
+              className="toast-view-btn toast-ignore-btn"
+              onClick={() => { onIgnoreUblock?.(); onDismiss(toast.id) }}
+            >
+              Ignore
+            </button>
+            <button
+              type="button"
+              className="toast-dismiss"
+              onClick={() => onDismiss(toast.id)}
+              aria-label="Dismiss"
+            >
+              ×
+            </button>
+          </div>
+        </div>
+        {expanded && (
+          <p className="toast-warning-detail">
+            {toast.text || 'ARCHIVR_UBLOCK=true but ARCHIVR_UBLOCK_EXT is not set or the path is invalid. The page was captured without ad-blocking. Set ARCHIVR_UBLOCK_EXT to the unpacked uBlock Origin Lite extension directory to enable ad-blocking, or set ARCHIVR_UBLOCK=false to silence this warning.'}
+          </p>
+        )}
+      </div>
+    )
+  }
+
   return (
     <div className="toast toast--error" role="alert" aria-atomic="true">
       <div className="toast-top">
@@ -36,7 +81,7 @@ function Toast({ toast, onDismiss }) {
           {short && <span className="toast-locator">{short}</span>}
         </div>
         <div className="toast-btns">
-          {toast.errorText && (
+          {toast.text && (
             <button
               type="button"
               className="toast-view-btn"
@@ -55,8 +100,8 @@ function Toast({ toast, onDismiss }) {
           </button>
         </div>
       </div>
-      {expanded && toast.errorText && (
-        <pre className="toast-error-detail">{toast.errorText}</pre>
+      {expanded && toast.text && (
+        <pre className="toast-error-detail">{toast.text}</pre>
       )}
     </div>
   )

frontend/src/styles.css

@@ -812,6 +812,7 @@ select {
   to   { opacity: 1; transform: translateY(0) scale(1); }
 }
 .toast--error { border-left: 3px solid var(--accent); }
+.toast--warning { border-left: 3px solid #e8a000; }
 
 .toast-top {
   display: flex;
@@ -892,6 +893,18 @@ select {
   max-height: 200px;
   overflow-y: auto;
 }
+.toast-warning-detail {
+  margin: 0;
+  padding: 10px 14px 12px;
+  font-size: 12px;
+  line-height: 1.55;
+  color: var(--muted);
+  background: var(--paper-2);
+  border-top: 1px solid var(--line);
+  white-space: pre-wrap;
+  word-break: break-word;
+}
+.toast-ignore-btn { color: var(--muted); }
 
 /* ── Utility ─────────────────────────────────────────────────────────────── */
 .muted { color: var(--muted); }