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/components/ContextRail.jsx

@@ -1,16 +1,17 @@
 import { useState, useEffect, useRef } from 'react'
 import { fetchEntryDetail, fetchEntryTags, assignTag, removeTag, listEntryCollections, updateEntryTitle } from '../api'
-import { formatTimestamp, formatBytes, valueText, sourceIconSvg } from '../utils'
+import { formatTimestamp, formatBytes, valueText, sourceIconSvg, displayPath } from '../utils'
 
 const VIS_LABEL = { 0: 'Private', 1: 'Public', 2: 'Users only', 3: 'Public' }
 
+
 const ExternalIcon = () => (
   <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
     <path d="M7 17 17 7M9 7h8v8"/>
   </svg>
 )
 
-export default function ContextRail({ archiveId, selectedEntry, onTagFilterSet, tagNodes, onTagsRefresh, onEntryTitleChange }) {
+export default function ContextRail({ archiveId, selectedEntry, onTagFilterSet, tagNodes, onTagsRefresh, onEntryTitleChange, humanizeTags }) {
   const [detail, setDetail] = useState(null)
   const [tags, setTags] = useState([])
   const [assignInput, setAssignInput] = useState('')
@@ -190,7 +191,7 @@ export default function ContextRail({ archiveId, selectedEntry, onTagFilterSet,
               <div className="tags-wrap">
                 {tags.map(tag => (
                   <span key={tag.tag_uid} className="tag-pill" title={tag.full_path}>
-                    {tag.name}
+                    {humanizeTags ? displayPath(tag.full_path) : tag.full_path}
                     <button
                       className="remove"
                       title={`Remove tag ${tag.full_path}`}