feat: implement entry deletion

- database: cascade_cached_bytes_after_subtree_delete — one-pass set-aware
  SQL that excludes the entire subtree simultaneously, avoiding sibling-blob
  cross-counting bug
- database: delete_entry — collects subtree IDs, runs set-aware cascade,
  NULLs archive_run_items.produced_entry_id (FK blocker), deletes children
  then root; ON DELETE CASCADE handles artifacts/tags/collections
- server: DELETE /api/archives/:archive_id/entries/:entry_uid route,
  wrapped in a transaction for atomicity
- frontend: deleteEntry API call, handleEntryDeleted callback in App.jsx
  (optimistic list removal + selection clear), Delete entry button in
  ContextRail with confirm guard
- tests: 4 database tests (unknown uid, subtree removal, run_item nulling,
  cached_bytes recalculation) + 3 route tests (204+gone, 404, 401)

frontend/src/App.jsx

@@ -212,6 +212,12 @@ export default function App() {
     )
   }, [])
 
+  const handleEntryDeleted = useCallback((entryUid) => {
+    setEntries(prev => prev.filter(e => e.entry_uid !== entryUid))
+    setSelectedEntry(prev => prev?.entry_uid === entryUid ? null : prev)
+    setSelectedEntryUid(prev => prev === entryUid ? null : prev)
+  }, [])
+
   const handleCaptureClick = useCallback(() => {
     setCaptureDialogOpen(true)
   }, [])
@@ -317,6 +323,7 @@ export default function App() {
             tagNodes={tagNodes}
             onTagsRefresh={handleTagsRefresh}
             onEntryTitleChange={handleEntryTitleChange}
+            onEntryDeleted={handleEntryDeleted}
             humanizeTags={humanizeTags}
           />
         </main>

frontend/src/api.js

@@ -58,6 +58,14 @@ export async function removeTag(archiveId, entryUid, tagUid) {
   if (!resp.ok) throw new Error(`Remove failed (${resp.status})`);
 }
 
+export async function deleteEntry(archiveId, entryUid) {
+  const resp = await fetch(
+    `/api/archives/${archiveId}/entries/${entryUid}`,
+    { method: 'DELETE' }
+  );
+  if (!resp.ok) throw new Error(`Delete failed (${resp.status})`);
+}
+
 export async function renameTag(archiveId, tagUid, name) {
   const res = await fetch(
     `/api/archives/${archiveId}/tags/${tagUid}`,

frontend/src/components/ContextRail.jsx

@@ -1,5 +1,5 @@
 import { useState, useEffect, useRef } from 'react'
-import { fetchEntryDetail, fetchEntryTags, assignTag, removeTag, listEntryCollections, updateEntryTitle } from '../api'
+import { fetchEntryDetail, fetchEntryTags, assignTag, removeTag, listEntryCollections, updateEntryTitle, deleteEntry } from '../api'
 import { formatTimestamp, formatBytes, valueText, sourceIconSvg, displayPath } from '../utils'
 
 const VIS_LABEL = { 0: 'Private', 1: 'Public', 2: 'Users only', 3: 'Public' }
@@ -11,7 +11,7 @@ const ExternalIcon = () => (
   </svg>
 )
 
-export default function ContextRail({ archiveId, selectedEntry, onTagFilterSet, tagNodes, onTagsRefresh, onEntryTitleChange, humanizeTags }) {
+export default function ContextRail({ archiveId, selectedEntry, onTagFilterSet, tagNodes, onTagsRefresh, onEntryTitleChange, onEntryDeleted, humanizeTags }) {
   const [detail, setDetail] = useState(null)
   const [tags, setTags] = useState([])
   const [assignInput, setAssignInput] = useState('')
@@ -86,6 +86,17 @@ export default function ContextRail({ archiveId, selectedEntry, onTagFilterSet,
     }
   }
 
+  async function handleDeleteEntry() {
+    if (!selectedEntry || !archiveId) return
+    if (!window.confirm('Delete this entry? This cannot be undone.')) return
+    try {
+      await deleteEntry(archiveId, selectedEntry.entry_uid)
+      onEntryDeleted?.(selectedEntry.entry_uid)
+    } catch {
+      // silently ignore — entry stays selected if delete failed
+    }
+  }
+
   const metaRows = detail ? [
     ['Added',      formatTimestamp(detail.summary.archived_at)],
     ['Source',     detail.summary.source_kind],
@@ -232,6 +243,12 @@ export default function ContextRail({ archiveId, selectedEntry, onTagFilterSet,
               ))}
             </div>
           )}
+
+          <div className="rail-delete-zone">
+            <button className="rail-delete-btn" onClick={handleDeleteEntry}>
+              Delete entry
+            </button>
+          </div>
         </>
       )}
     </aside>

frontend/src/styles.css

@@ -527,6 +527,31 @@ select {
   background: var(--accent-2);
 }
 
+/* ── Rail delete zone ───────────────────────────────────────────────────── */
+.rail-delete-zone {
+  margin-top: 24px;
+  padding-top: 20px;
+  border-top: 1px solid var(--line-soft);
+}
+.rail-delete-btn {
+  width: 100%;
+  padding: 8px 14px;
+  background: none;
+  border: 1px solid color-mix(in srgb, var(--accent) 45%, transparent);
+  color: var(--accent);
+  border-radius: var(--r);
+  cursor: pointer;
+  font-size: 12.5px;
+  font-weight: 600;
+  letter-spacing: 0.04em;
+  text-transform: uppercase;
+  transition: background 0.15s ease, border-color 0.15s ease;
+}
+.rail-delete-btn:hover {
+  background: color-mix(in srgb, var(--accent) 8%, transparent);
+  border-color: var(--accent);
+}
+
 /* ── Capture dialog ──────────────────────────────────────────────────────── */
 .capture-dialog {
   border: 1px solid var(--line);