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/styles.css

@@ -673,6 +673,56 @@ select {
 .tag-node-btn:hover { text-decoration: underline; }
 .tag-node-btn.is-active { font-weight: 600; color: var(--ink); }
 
+/* tag-node-row: flex row containing the name button + delete × */
+.tag-node-row {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+}
+.tag-node-row .tag-node-btn {
+  flex: 1 1 0;
+  min-width: 0;
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  width: auto;
+}
+/* constrain the edit pencil so it doesn't inherit unconstrained SVG dimensions */
+.tag-node-btn .edit-icon {
+  width: 0.75em;
+  height: 0.75em;
+  flex-shrink: 0;
+  vertical-align: -0.1em;
+  opacity: 0.35;
+}
+.tag-node-btn:hover .edit-icon { opacity: 0.65; }
+/* delete × button next to tag name — small, unobtrusive */
+.tag-node-delete {
+  flex-shrink: 0;
+  border: 0;
+  background: transparent;
+  color: var(--muted-2);
+  cursor: pointer;
+  padding: 0 3px;
+  font-size: 14px;
+  line-height: 1;
+  opacity: 0;
+}
+.tag-node-row:hover .tag-node-delete { opacity: 1; }
+.tag-node-delete:hover { color: var(--accent); }
+/* rename input inside the tag list */
+.tag-rename-input {
+  font-size: 13px;
+  flex: 1 1 0;
+  min-width: 0;
+  padding: 2px 5px;
+  border: 1px solid var(--accent);
+  border-radius: var(--r);
+  background: var(--field);
+  color: var(--ink);
+  outline: none;
+}
+
 /* ── Collections page (sidebar layout) ──────────────────────────────────── */
 .collections-view {
   padding: 24px;