feat: tag delete, rename, and per-user humanize-tags display setting (#16)

* feat: add tag delete and rename (backend + frontend)

- DELETE /api/archives/:id/tags/:tag_uid — deletes tag subtree via
  recursive CTE; entry_tag_assignments cascade automatically
- PATCH  /api/archives/:id/tags/:tag_uid { name } — renames a tag
  segment (case-preserving slug), cascades full_path to all descendants
  in one transaction using hierarchy CTE (not LIKE), returns updated Tag
- database: rename_tag + delete_tag with 7 unit tests covering subtree
  cascade, collision detection, descendant path rewrite, slug stripping
- TagsView: inline rename (pencil icon / double-click → input), × delete
  with confirmation dialog (warns about child tags)
- App.jsx: handleTagRenamed rewrites tagFilter for exact + descendant
  paths; handleTagDeleted clears filter for deleted subtree
- api.js: renameTag (PATCH, returns Tag) + deleteTag (DELETE)
- ContextRail: tag pills show displayPath(full_path) (humanized) with
  raw full_path in title tooltip; humanize-tags setting coming next

* feat: per-user humanize-tags display setting

- auth DB: idempotent migration adds users.humanize_slugs INTEGER DEFAULT 0
- GET /api/auth/me: returns humanize_slugs bool
- PATCH /api/auth/me: accepts { humanize_slugs: bool }, persisted via
  database::update_user_humanize_slugs
- displayPath() helper moved to utils.js (was local to ContextRail)
- TagsView: node label shows tag.name vs tag.slug based on humanizeTags
- ContextRail: pill label applies displayPath conditionally
- App.jsx: derives humanizeTags from currentUser.humanize_slugs, passes
  to TagsView + ContextRail; filter badge label humanized when on
- Settings > Profile: Display Preferences section with checkbox toggle,
  updates backend and currentUser immediately via setCurrentUser
- api.js: patchMe(patch) for generic PATCH /api/auth/me
- Tests: auth_me default=false, PATCH persists=true (2 route tests)

frontend/src/api.js

@@ -58,6 +58,27 @@ export async function removeTag(archiveId, entryUid, tagUid) {
   if (!resp.ok) throw new Error(`Remove failed (${resp.status})`);
 }
 
+export async function renameTag(archiveId, tagUid, name) {
+  const res = await fetch(
+    `/api/archives/${archiveId}/tags/${tagUid}`,
+    {
+      method: 'PATCH',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ name }),
+    }
+  );
+  if (!res.ok) throw new Error(await res.text());
+  return res.json(); // returns the updated Tag: { tag_uid, name, slug, full_path }
+}
+
+export async function deleteTag(archiveId, tagUid) {
+  const res = await fetch(
+    `/api/archives/${archiveId}/tags/${tagUid}`,
+    { method: 'DELETE' }
+  );
+  if (!res.ok) throw new Error(await res.text());
+}
+
 export async function fetchRuns(archiveId) {
   return getJson(`/api/archives/${archiveId}/runs`);
 }
@@ -132,6 +153,15 @@ export async function updateProfile(displayName) {
   if (!res.ok) throw new Error(await res.text());
 }
 
+export async function patchMe(patch) {
+  const res = await fetch('/api/auth/me', {
+    method: 'PATCH',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(patch),
+  });
+  if (!res.ok) throw new Error(await res.text());
+}
+
 export async function changePassword(currentPassword, newPassword) {
   const res = await fetch('/api/auth/me', {
     method: 'PATCH',