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/api.js

@@ -0,0 +1,70 @@
+async function getJson(url) {
+  const response = await fetch(url);
+  if (!response.ok) {
+    throw new Error(`${response.status} ${response.statusText}`);
+  }
+  return response.json();
+}
+
+export async function fetchArchives() {
+  return getJson("/api/archives");
+}
+
+export async function fetchEntries(archiveId) {
+  return getJson(`/api/archives/${archiveId}/entries`);
+}
+
+export async function searchEntries(archiveId, q, tag) {
+  const params = new URLSearchParams();
+  if (q) params.set("q", q);
+  if (tag) params.set("tag", tag);
+  return getJson(`/api/archives/${archiveId}/entries/search?${params}`);
+}
+
+export async function fetchEntryDetail(archiveId, entryUid) {
+  return getJson(`/api/archives/${archiveId}/entries/${entryUid}`);
+}
+
+export async function fetchEntryTags(archiveId, entryUid) {
+  return getJson(`/api/archives/${archiveId}/entries/${entryUid}/tags`);
+}
+
+export async function assignTag(archiveId, entryUid, tagPath) {
+  const resp = await fetch(
+    `/api/archives/${archiveId}/entries/${entryUid}/tags`,
+    {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ tag_path: tagPath }),
+    }
+  );
+  if (!resp.ok) throw new Error(`Failed to add tag (${resp.status})`);
+}
+
+export async function removeTag(archiveId, entryUid, tagUid) {
+  const resp = await fetch(
+    `/api/archives/${archiveId}/entries/${entryUid}/tags/${tagUid}`,
+    { method: "DELETE" }
+  );
+  if (!resp.ok) throw new Error(`Remove failed (${resp.status})`);
+}
+
+export async function fetchRuns(archiveId) {
+  return getJson(`/api/archives/${archiveId}/runs`);
+}
+
+export async function fetchTags(archiveId) {
+  return getJson(`/api/archives/${archiveId}/tags`);
+}
+
+export async function submitCapture(archiveId, locator) {
+  const res = await fetch(`/api/archives/${archiveId}/captures`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify({ locator }),
+  });
+  if (!res.ok) {
+    const msg = await res.text();
+    throw new Error(msg || `HTTP ${res.status}`);
+  }
+}