feat(ui): rewrite frontend in React with Vite

- Scaffold Vite+React project in frontend/ (bun, react 18, @vitejs/plugin-react)
- vite.config.js outputs to crates/archivr-server/static/ directly
- src/utils.js: formatBytes, valueText, formatTimestamp, SOURCE_ICONS, sourceIconSvg
- src/api.js: typed fetch wrappers for all API endpoints
- App.jsx: full state management, archive switching, debounced search,
  tag filter, view routing, capture dialog orchestration
- components/Topbar.jsx: archive switcher, nav, capture button
- components/CaptureDialog.jsx: native <dialog> ref with showModal/close,
  Escape key support, locator validation
- components/EntriesView.jsx + EntryRow.jsx: flex table with source icons,
  type pills, keyboard selection
- components/ContextRail.jsx: parallel detail+tags fetch, stale-race guard
  via selectSeqRef, inline tag assign/remove
- components/RunsView.jsx: runs kept as <table> (matches original)
- components/AdminView.jsx: mounted archives list
- components/TagsView.jsx: recursive tag tree with active state
- Remove old app.js; styles.css moved to frontend/src/ (Vite bundles it)

frontend/src/components/CaptureDialog.jsx

@@ -0,0 +1,65 @@
+import { useRef, useEffect, useState } from 'react'
+import { submitCapture } from '../api'
+
+export default function CaptureDialog({ open, archiveId, onClose, onCaptured }) {
+  const dialogRef = useRef(null)
+  const [locator, setLocator] = useState('')
+  const [error, setError] = useState(null)
+  const [busy, setBusy] = useState(false)
+
+  useEffect(() => {
+    const dialog = dialogRef.current
+    if (!dialog) return
+    const handleClose = () => onClose()
+    dialog.addEventListener('close', handleClose)
+    return () => dialog.removeEventListener('close', handleClose)
+  }, [onClose])
+
+  useEffect(() => {
+    const dialog = dialogRef.current
+    if (!dialog) return
+    if (open) {
+      setLocator('')
+      setError(null)
+      if (!dialog.open) dialog.showModal()
+    } else {
+      if (dialog.open) dialog.close()
+    }
+  }, [open])
+
+  async function handleSubmit() {
+    if (!locator.trim()) { setError('Enter a locator.'); return }
+    setBusy(true)
+    setError(null)
+    try {
+      await submitCapture(archiveId, locator.trim())
+      dialogRef.current?.close()
+      onCaptured()
+    } catch (e) {
+      setError(e.message)
+    } finally {
+      setBusy(false)
+    }
+  }
+
+  return (
+    <dialog ref={dialogRef} className="capture-dialog">
+      <div className="capture-dialog-inner">
+        <h2 className="capture-dialog-title">Capture</h2>
+        <label htmlFor="capture-locator" className="capture-label">Locator</label>
+        <input id="capture-locator" className="capture-input" type="text"
+          placeholder="tweet:1234567890 or https://..."
+          value={locator} onChange={e => setLocator(e.target.value)}
+          onKeyDown={e => { if (e.key === 'Enter') handleSubmit() }}
+          autoComplete="off" />
+        {error && <div className="capture-error">{error}</div>}
+        <div className="capture-actions">
+          <button type="button" className="capture-cancel" onClick={() => dialogRef.current?.close()}>Cancel</button>
+          <button type="button" className="capture-submit" onClick={handleSubmit} disabled={busy}>
+            {busy ? 'Capturing\u2026' : 'Capture'}
+          </button>
+        </div>
+      </div>
+    </dialog>
+  )
+}