Wiki Phase 3: internal links, backlinks, and tags

Connectivity phase of the wiki upgrade (see WIKI_UPGRADE.md).

Schema (additive new tables): wiki_tags, wiki_page_tags, wiki_links.

Internal links & backlinks:
- new wiki.links.js parses a saved body for /wiki/<slug> (and data-wiki-slug)
  targets; wiki_links is rebuilt on every save
- article shows a "Linked from" section (published backlinks) and renders
  links to non-existent pages as red links (server returns missing_links)
- editor gains an internal-link picker listing existing pages

Tags:
- pages accept a tags[] array; tags upsert on save, page tag-set is replaced,
  and orphaned tags are auto-pruned (on save and delete)
- public/admin list filter by ?tag=; /wiki/tags lists tags with published counts
- article shows tag chips; the index has a flat tag-filtered view; editor has a
  comma-separated tags field

Verified end-to-end: A->B backlink appears, red link detected, link index
rebuilds on edit, tag filtering + chips + pruning all work.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/router/v1/admin/admin.controller.js

@@ -177,6 +177,10 @@ async function listWiki(req, res) {
       const category = await wiki.getCategoryBySlug(req.query.category)
       filters.categoryId = category ? category.id : -1 // unknown → match nothing
     }
+    if (req.query.tag) {
+      const tag = await wiki.getTagBySlug(req.query.tag)
+      filters.tagId = tag ? tag.id : -1 // unknown → match nothing
+    }
     if (req.query.status === 'draft') filters.published = false
     if (req.query.status === 'published') filters.published = true
     return res.json(await wiki.listAll(filters))
@@ -221,6 +225,7 @@ async function createWiki(req, res) {
       excerpt: req.body.excerpt || null,
       categoryId: cat.value,
       published: req.body.published !== false,
+      tags: Array.isArray(req.body.tags) ? req.body.tags : undefined,
       updatedBy: req.user.id,
     })
     await activity.log({ req, action: 'wiki.create', detail: { slug: page.slug } })
@@ -241,6 +246,7 @@ async function updateWiki(req, res) {
     if ('body' in req.body) input.body = req.body.body || null
     if ('excerpt' in req.body) input.excerpt = req.body.excerpt || null
     if ('published' in req.body) input.published = Boolean(req.body.published)
+    if ('tags' in req.body) input.tags = Array.isArray(req.body.tags) ? req.body.tags : []
     if ('category_id' in req.body) {
       const cat = await resolveCategoryId(req.body)
       if (!cat.ok) return res.status(400).json({ message: 'Unknown category' })
@@ -282,6 +288,15 @@ async function deleteWiki(req, res) {
   }
 }
 
+// ── Wiki tags ──────────────────────────────────────────────────────────
+async function listWikiTags(req, res) {
+  try {
+    return res.json(await wiki.listTags())
+  } catch (err) {
+    return res.status(500).json({ message: 'Internal Server Error' })
+  }
+}
+
 // ── Wiki categories ────────────────────────────────────────────────────
 async function listWikiCategories(req, res) {
   try {
@@ -473,6 +488,7 @@ module.exports = {
   updateWiki,
   publishWiki,
   deleteWiki,
+  listWikiTags,
   listWikiCategories,
   createWikiCategory,
   updateWikiCategory,

server/src/router/v1/admin/admin.routes.js

@@ -90,6 +90,9 @@ adminRouter.put(
 )
 adminRouter.delete('/wiki/categories/:id', param('id').isInt(), validate, ctrl.deleteWikiCategory)
 
+// ── Wiki tags ──────────────────────────────────────────────────────────
+adminRouter.get('/wiki/tags', ctrl.listWikiTags)
+
 // ── Wiki pages ─────────────────────────────────────────────────────────
 adminRouter.get('/wiki', ctrl.listWiki)
 adminRouter.post(
@@ -99,6 +102,7 @@ adminRouter.post(
   body('excerpt').optional({ values: 'falsy' }).isString().isLength({ max: 400 }),
   body('category_id').optional({ values: 'null' }).isInt(),
   body('published').optional().isBoolean(),
+  body('tags').optional().isArray(),
   validate,
   ctrl.createWiki,
 )
@@ -109,6 +113,7 @@ adminRouter.put(
   body('excerpt').optional({ values: 'falsy' }).isString().isLength({ max: 400 }),
   body('category_id').optional({ values: 'null' }).isInt(),
   body('published').optional().isBoolean(),
+  body('tags').optional().isArray(),
   validate,
   ctrl.updateWiki,
 )