refactor(routes): move note domain into routes/note/ subpackage (#5236)

Slice 2f of the route-domain reorganization (#4082/#4071, per
specs/architecture-runtime-inventory.md §6.3). Moves note_routes.py into
routes/note/, leaving a backward-compat sys.modules shim at the old path.
Pure file reorganization, no behavior change.

The shim uses sys.modules replacement (same pattern as the merged gallery
#4903, research #4975, memory #5007, history #5090, and contacts #5227
slices) so that `import routes.note_routes`, `from routes.note_routes import
X`, `importlib.import_module(...)`, and the `import ... as note_routes` +
`monkeypatch.setattr(note_routes, "SessionLocal", ...)` pattern used by
test_note_reminder_fire_scope.py / test_notes_fail_closed_auth.py all
operate on the same module object the application uses.

The canonical module does NOT depend on the shim — routes/note/note_routes.py
imports only from core/, src/, and stdlib. The outbound email cross-domain
imports (routes.email_routes._get_email_config, routes.email_helpers.
_send_smtp_message) are function-local lazy imports that keep resolving
through the email module's own path (email is not yet migrated).

One source-introspection test site repointed to the new canonical path:
- test_model_helper_owner_scope.py (shared with history; history entry
  already repointed in #5090, note entry repointed here)

Adds tests/test_note_routes_shim.py to pin the sys.modules shim contract
(legacy and canonical paths resolve to the same module object; monkeypatch
via legacy alias reaches the canonical module).

Verified: compileall clean; full suite 4487 passed, 3 skipped.

app.py

@@ -830,7 +830,7 @@ app.include_router(setup_api_token_routes())
 logger.info("Webhook & API token routes initialized")
 
 # Notes (Google Keep-style notes/todos)
-from routes.note_routes import setup_note_routes
+from routes.note.note_routes import setup_note_routes
 app.include_router(setup_note_routes(task_scheduler, upload_handler=upload_handler))
 
 # Email