Feat v0.4.3 backlinks wikilinks

Obsidian-style [[wikilinks]] for the notes surface. New ext_notes_links
table (source_id, target_id, link_text) with bidirectional indexes.

Backend: _extract_wikilinks() parses [[...]] via split (no regex in
Starlark). _sync_links() on create/update resolves titles to note IDs.
Cascade delete cleans both directions. GET /links/:id and
GET /backlinks/:id endpoints.

Frontend: wikilinks render as clickable links in preview — blue for
resolved, red for unresolved. Clicking resolved navigates; clicking
unresolved creates the note and re-saves source to resolve the link.
BacklinksPanel shows incoming links below editor with click navigation.

Notes package 0.3.0 → 0.4.0.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/notes/manifest.json

@@ -6,7 +6,7 @@
   "route": "/s/notes",
   "auth": "authenticated",
   "layout": "single",
-  "version": "0.3.0",
+  "version": "0.4.0",
   "icon": "📝",
   "description": "Markdown notes surface with folders, tags, and backlinks.",
   "author": "switchboard",
@@ -28,7 +28,9 @@
     {"method": "POST",   "path": "/notes/move"},
     {"method": "GET",    "path": "/tags"},
     {"method": "GET",    "path": "/tags/*"},
-    {"method": "PUT",    "path": "/tags/*"}
+    {"method": "PUT",    "path": "/tags/*"},
+    {"method": "GET",    "path": "/links/*"},
+    {"method": "GET",    "path": "/backlinks/*"}
   ],
 
   "db_tables": {
@@ -59,6 +61,17 @@
         ["tag"]
       ]
     },
+    "links": {
+      "columns": {
+        "source_id": "text",
+        "target_id": "text",
+        "link_text": "text"
+      },
+      "indexes": [
+        ["source_id"],
+        ["target_id"]
+      ]
+    },
     "folders": {
       "columns": {
         "name":       "text",