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.

core/src/local/schema.rs

@@ -1,7 +1,8 @@
 //! Local SQLite schema + migrations. The schema mirrors the note/label model so an
 //! offline note can later sync 1:1 with the server. Each syncable row carries local
 //! `sync_revision` + `dirty` bookkeeping (consumed by the sync engine in M10.7);
-//! `[[links]]` are NOT stored (derived at query time), matching docs/sync.md.
+//! `#tags` are NOT stored as such (derived at query time into labels), matching
+//! docs/sync.md.
 //!
 //! Migrations are gated on `PRAGMA user_version`; bump it and add a block per change.