Remove [[wiki-links]], backlinks and the graph

Operator, 2026-08-22 (note 2897): ThoughtSync is an intermediary surface. You
write here because it's easy — a notebook in your pocket — and later you recall
the thing and go finish it somewhere else. Recall is the product; organization
is secondary. A linking system is organization, and it isn't what this is for.

So: `[[wiki-links]]`, backlinks, the `[[` autocomplete, the note_links table,
`/api/notes/link-search`, `/api/notes/<id>/backlinks`, the whole graph blueprint
and GraphView. Rust core loses `extract_links`, `backlinks`, `link_search` and
`create_titled`; the desktop loses the three Tauri commands that exposed them.

This subsumes 982d24c rather than reverting it. That commit bound links to a
note id so a rename would stop rewriting other notes' bodies — real infra, but
infra for a feature that is now gone, and nothing it added survives. Alembic
0023 stays in the chain anyway: it shipped in an image and may already be
applied, and deleting an applied revision strands a database's version pointer.
0024 drops the table and takes the column with it. The history stays honest
about the fact that it existed for a day.

Two things deliberately kept, because they were serving recall and only
incidentally serving links:

- `/api/notes/titles` and the titles store. The command palette lists them so
  you can jump to a note by name. `resolve()` — the name→note lookup that only
  linking needed — is gone.
- `display_title`. Every note still has a name for search results and export
  filenames. What that name is FOR changed; that it exists did not.

`notes/links.py` is now `notes/tags.py`, holding the #tag→label reconciliation
it always also owned. A file called links.py with no links in it would have been
exactly the drift this removal is meant to end.

Also swept out on the way: `_escape_like`, whose only caller was link-search,
and the `graph` icon. Nothing lost that a person typed — note_links was always
derived, and the `[[text]]` is still sitting in every body it was written in.

docs/sync.md

@@ -122,9 +122,9 @@ as `?since=`. `since=0` (or absent) is a **full initial sync**.
   so pulling the note re-syncs the whole thing.
 - **Label** — the label *catalog* (name + color) syncs as its own entity so a
   rename/recolor/delete propagates independently of notes.
-- **Derived, NOT synced:** `[[wiki-links]]` and `#tags` are parsed from the note
-  body. Clients recompute them locally; the server recomputes them on push. They
-  never travel over the wire.
+- **Derived, NOT synced:** `#tags` are parsed from the note body. Clients recompute
+  them locally; the server recomputes them on push. They never travel over the wire.
+  (`[[wiki-links]]` were derived the same way until they were removed — note 2897.)
 - **Attachment blobs** sync by id over the existing upload/download routes (see
   Attachments below); only their metadata rides the delta feed.
 
@@ -201,7 +201,7 @@ Body: `{ "changes": [ ... ] }` (max 1000 per batch). Each change:
 - **Whole-note semantics.** A note upsert carries the client's *full* current
   state (not a partial patch) — the server overwrites all scalar fields, replaces
   items, and sets manual label memberships from `label_ids` (tag-sourced labels
-  are re-derived from the body). `[[links]]`/`#tags` are recomputed server-side.
+  are re-derived from the body). `#tags` are recomputed server-side.
 - **`op: "delete"`** purges (tombstones) the row. Trashing is just an upsert with
   `trashed: true`.
 - **Labels:** `{entity: "label", op: "upsert"|"delete", id, edited_at, name,