desktop M10.4: Rust local SQLite store + Tauri commands

The on-device core that makes the desktop app work with no server and no login.

- rusqlite (bundled SQLite, so no system libsqlite dependency to vary across
  builds); uuid v4 ids; RFC3339/Date.toISOString-compatible timestamps.
- Schema mirroring the note model: notes, labels, note_labels (with via_tag),
  checklist_items, attachments, link_previews, note_revisions, saved_filters,
  plus per-row sync_revision/dirty + a sync_state row for the M10.7 engine.
  user_version-gated migrations.
- derive.rs: pure [[wiki-link]] + #tag scanners (mirror the frontend inline
  rules, no regex dep) with unit tests; #tags re-sync via_tag labels on save,
  [[links]] drive backlinks at query time (derived, never stored).
- store.rs: the full repository surface (facet/label/date/text list, create,
  PATCH-semantics update, pin/archive/color/kind, checklist items, labels CRUD
  + merge, reminders complete/snooze, reorder, trash/restore/delete, revisions
  + restore, titles/search/backlinks/link-search, saved filters).
- commands.rs: ~38 #[tauri::command]s over a Mutex<Connection> in managed state.
- lib.rs: opens the DB in the platform app-data dir on setup; synthetic offline
  config/user so the auth-gated router resolves with no login.

Attachment upload / URL unfurl / import are intentionally deferred (network/file
concerns); adapters/local.ts (M10.5) wires all of the above via invoke.

Task 1993.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

desktop/src-tauri/src/local/mod.rs

@@ -0,0 +1,26 @@
+//! The local-first core: an on-device SQLite store + Tauri commands implementing the
+//! frontend's repository seam, so the desktop app is fully usable with no server and
+//! no login. adapters/local.ts (M10.5) calls into `commands`.
+
+pub mod commands;
+pub mod derive;
+pub mod models;
+pub mod schema;
+pub mod store;
+
+use std::path::Path;
+use std::sync::Mutex;
+
+use rusqlite::Connection;
+
+/// The shared database handle, held in Tauri's managed state. rusqlite connections
+/// aren't `Sync`, so a `Mutex` serializes access (fine — operations are quick and the
+/// UI is single-user).
+pub struct Db(pub Mutex<Connection>);
+
+/// Open (creating if needed) the database at `path` and bring it to the latest schema.
+pub fn open(path: &Path) -> rusqlite::Result<Db> {
+    let conn = Connection::open(path)?;
+    schema::migrate(&conn)?;
+    Ok(Db(Mutex::new(conn)))
+}