v0.2.0 (10/N): bridge:export console command + QML hook

PLAN.md §12 *Data backup / export* called for "a bridge:export console
command and a UI hook for backup-to-file from v1". Shipping both now
so the v0.2.0 surface has the data-portability story end-to-end:

PHP side — `bin/console bridge:export <destination>`:
- Reads the source path from DATABASE_URL so it works in dev mode
  (developer's source-tree var/data.sqlite) and bundled mode (user
  data dir SQLite) without environment-aware logic.
- SQLite-only by design (PLAN.md §6 — single-instance SQLite-first);
  emits a clear error for non-sqlite:// URLs rather than pretending
  to support drivers that need driver-specific dump tooling.
- Overwrites the destination if it exists (the FileDialog or shell
  redirect that produced the path has already confirmed).
- 4 unit tests: happy path, non-SQLite URL, missing source,
  overwrite. Test count 24 → 28.

QML side — Q_INVOKABLE BackendConnection.exportDatabase(path):
- Bundled mode only; dev mode emits databaseExportFailed and
  returns false (developers own their SQLite directly).
- Accepts both filesystem paths and `file://` URLs (FileDialog
  results).
- Returns synchronously with bool but also emits async signals
  databaseExported(dst) / databaseExportFailed(reason) so QML
  can drive a snackbar / log without polling the return value.
- Removes any existing destination first (QFile::copy refuses
  to overwrite); the picker has already confirmed the choice.

Drive-by: parse_url() rejects sqlite:///abs/path on PHP 8.5+ (the
host-less triple-slash trips its strictness). Switched to a
prefix-strip — Doctrine DBAL only emits two URL shapes for
SQLite anyway (sqlite:///abs and sqlite://relative).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -19,6 +19,7 @@ This section tracks work landing on `dev` toward **v0.2.0** (next minor; pre-1.0
 - **`make:bridge:event <Name>` maker.** Generates a domain-event class (`src/Event/<Name>Event.php`, readonly value object), a subscriber (`src/EventSubscriber/<Name>Subscriber.php`) that republishes via `PublisherInterface` on `app://event/<kebab-name>`, and a QML stub (`{qml_path}/<Name>EventHandler.qml`) that listens via `MercureClient` and re-emits as a typed `signal`. Closes the third row of PLAN.md §8's makers table; pairs with the existing `make:bridge:resource` / `command` / `window` makers so domain events have a one-command path from PHP through to QML.
 - **`make:bridge:read-model <Name>` maker.** Generates a query-only projection: `src/ReadModel/<Name>ReadModel.php` (query service stub injecting `EntityManagerInterface`), `src/Controller/<Name>Controller.php` (single GET handler at `/api/<kebab-plural>`), and `{qml_path}/<Name>List.qml` (`ReactiveListModel` bound to the route, deliberately *no* Mercure topic — read-models aren't auto-reactive; invalidation is event-driven via `make:bridge:event`). Closes the fourth row of PLAN.md §8's makers table.
 - **Pre-migration auto-backup of `var/data.sqlite`.** Bundled-mode supervisor copies the SQLite file to `var/data.sqlite.<unix-timestamp>.bak` before invoking `doctrine:migrations:migrate`; trims to the 5 most recent. SQLite's lack of transactional DDL means a half-applied migration can corrupt the database with no rollback path; cheap insurance against that. Skipped on first launch (no DB to back up); failure to copy logs a warning and continues (a missing safety-net is not a reason to refuse to boot). Backup runs only in bundled mode — dev mode users own their `var/data.sqlite` lifecycle. Bundled-supervisor integration test gained an assertion that a `.bak` file appears under the user data dir on second launch.
+- **`bridge:export` console command + QML hook.** New `bin/console bridge:export <destination>` copies the active SQLite database to a user-chosen path (overwrites if the destination exists; reads the source path from `DATABASE_URL` so it works in both dev and bundled mode). Mirrored on the QML side as `BackendConnection.exportDatabase(path)` (`Q_INVOKABLE bool`) returning success synchronously and emitting `databaseExported(path)` / `databaseExportFailed(reason)` for async UX. QML callers typically pair it with `Qt.labs.platform.FileDialog` (see `docs/native-dialogs.md`). 4 unit tests cover the command's success / non-SQLite-URL / missing-source / overwrite paths.
 
 ### Changed