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>

framework/php/src/Command/BridgeExportCommand.php

@@ -0,0 +1,109 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpQml\Bridge\Command;
+
+use Symfony\Component\Console\Attribute\AsCommand;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Console\Style\SymfonyStyle;
+use Symfony\Component\DependencyInjection\Attribute\Autowire;
+
+/**
+ * Copies the active SQLite database to a destination path. Paired with
+ * the QML `BackendConnection.exportDatabase()` hook so end users can
+ * "Export my data" before a machine move or before authorising a
+ * risky migration.
+ *
+ * Driven from `DATABASE_URL` so it works identically in dev mode
+ * (developer's source-tree var/data.sqlite) and bundled mode (user
+ * data dir under XDG/Library/AppData). Non-SQLite drivers are out
+ * of scope — exposing them would require driver-specific dump
+ * tooling and the framework is single-instance SQLite-first by
+ * design (PLAN.md §6).
+ */
+#[AsCommand(
+    name: 'bridge:export',
+    description: 'Copy the SQLite database to a destination path (snapshot, not a live dump).',
+)]
+final class BridgeExportCommand extends Command
+{
+    public function __construct(
+        #[Autowire('%env(default::DATABASE_URL)%')]
+        private readonly string $databaseUrl,
+    ) {
+        parent::__construct();
+    }
+
+    protected function configure(): void
+    {
+        $this->addArgument(
+            'destination',
+            InputArgument::REQUIRED,
+            'Where to write the exported file (overwrites if it exists).',
+        );
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output): int
+    {
+        $io = new SymfonyStyle($input, $output);
+
+        $source = $this->resolveSqlitePath();
+        if (null === $source) {
+            $io->error([
+                'DATABASE_URL is not a sqlite:/// URL.',
+                'bridge:export only handles SQLite — other drivers need driver-specific dumps.',
+            ]);
+
+            return Command::FAILURE;
+        }
+        if (!is_file($source)) {
+            $io->error("SQLite file does not exist: {$source}");
+
+            return Command::FAILURE;
+        }
+
+        $destination = (string) $input->getArgument('destination');
+        if ('' === $destination) {
+            $io->error('Destination path cannot be empty.');
+
+            return Command::FAILURE;
+        }
+
+        // Snapshot semantics: for a *running* application, SQLite's WAL
+        // journal may hold uncommitted writes that a plain copy misses.
+        // The desktop case is single-process, single-writer; flushing
+        // is a no-op here (Doctrine commits per request, no long-running
+        // transactions). If that ever changes, swap to `sqlite3_backup`
+        // via PDO::sqliteCreateFunction for a consistent online copy.
+        if (!@copy($source, $destination)) {
+            $err = error_get_last()['message'] ?? 'unknown error';
+            $io->error("Could not copy {$source} → {$destination}: {$err}");
+
+            return Command::FAILURE;
+        }
+
+        $io->success("Exported {$source} → {$destination}.");
+
+        return Command::SUCCESS;
+    }
+
+    private function resolveSqlitePath(): ?string
+    {
+        // parse_url() rejects `sqlite:///abs/path` (host-less triple-slash)
+        // on PHP 8.5+, so do the strip manually. Doctrine's DBAL only
+        // emits two URL shapes for SQLite: sqlite:///abs/path (absolute,
+        // PLAN.md §3 *Startup* uses this) and sqlite://relative/path.
+        if (str_starts_with($this->databaseUrl, 'sqlite:///')) {
+            return '/'.substr($this->databaseUrl, \strlen('sqlite:///'));
+        }
+        if (str_starts_with($this->databaseUrl, 'sqlite://')) {
+            return substr($this->databaseUrl, \strlen('sqlite://'));
+        }
+
+        return null;
+    }
+}