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/public/public.controller.js

@@ -58,15 +58,28 @@ async function getWikiCategories(req, res) {
   }
 }
 
+async function getWikiTags(req, res) {
+  try {
+    return res.json(await wiki.listTags())
+  } catch (err) {
+    return res.status(500).json({ message: 'Internal Server Error' })
+  }
+}
+
 async function getWikiList(req, res) {
   try {
-    let categoryId = null
+    const filters = {}
     if (req.query.category) {
       const category = await wiki.getCategoryBySlug(req.query.category)
       if (!category) return res.json([]) // unknown category → no pages
-      categoryId = category.id
+      filters.categoryId = category.id
     }
-    return res.json(await wiki.listPublished(categoryId))
+    if (req.query.tag) {
+      const tag = await wiki.getTagBySlug(req.query.tag)
+      if (!tag) return res.json([]) // unknown tag → no pages
+      filters.tagId = tag.id
+    }
+    return res.json(await wiki.listPublished(filters))
   } catch (err) {
     return res.status(500).json({ message: 'Internal Server Error' })
   }
@@ -100,6 +113,7 @@ module.exports = {
   getPosts,
   getPost,
   getWikiCategories,
+  getWikiTags,
   getWikiList,
   getWikiPage,
   contact,