untested... test: add unit test suite and CI workflow

I have never done this style of test before... who knows if it will work

- Add Gitea Actions workflow for PHP 8.2 testing
- Add PHPUnit configuration and bootstrap file
- Add unit tests for TalkService, WebhookController, ImageCleanup, NavigationProvider, and DebugToggle
- Add README documentation for the test suite
- Update composer.json with test and lint scripts

tests/README.md

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+# nc_bot_webhooks Test Suite
+
+## Running Tests Locally
+
+```bash
+cd nc_bot_webhooks
+composer install
+composer test
+```
+
+## Requirements
+
+- PHP 8.2+
+- Composer
+
+## What Each Test File Covers
+
+### `TalkServiceTest.php`
+
+Unit tests for `Service/TalkService.php` business logic. All TalkService constructor dependencies are mocked via `PHPUnit\Framework\TestCase::getMockForTrait()`.
+
+**Test groups:**
+
+- **validateBotPassword** — empty string, valid password, special chars, unicode
+- **getBaseUrl** — overwritehost priority, overwritewebroot, trusted_domains filtering, CLI URL fallback, empty config
+- **getRooms / setRooms** — JSON persistence round-trip, empty config, invalid JSON
+- **getAuthTokens / setAuthTokens** — JSON persistence, empty config
+- **validateAuthToken** — valid token, invalid token, nonexistent room, multiple tokens
+- **generateAuthToken** — 48-char hex token, uniqueness across calls
+- **revokeAuthToken** — removes specific token, cleans empty room arrays, nonexistent token
+- **mapPayload** — content only, embeds with title/description/fields, empty payload, multiple embeds
+- **mapApprisePayload** — body only, title fallback, type icons, image type with attachments, nested data key
+- **getSenderName** — sender_name > username > config default priority
+- **getSenderNameDefault** — config default
+- **prependDisplayName** — with/without message, with type icon
+- **downloadImage** — successful download, empty body
+- **purgeOldImages** — files older/newer than cutoff, empty directory, bot user not found
+
+### `WebhookControllerTest.php`
+
+Unit tests for `Controller/WebhookController.php` HTTP endpoints. Tests response codes and headers for the controller methods that don't depend on `php://input` (auth validation and room listing), plus fallback paths that use `$_GET` and `$_POST` directly.
+
+**Test groups:**
+
+- **receive** — invalid auth token (401), empty body (400), $_GET fallback with content, $_GET fallback with embeds
+- **receiveApprise** — invalid auth token (401), empty body (400), $_POST fallback with notifications, $_POST with image type, $_GET fallback with notifications
+- **receiveAppriseNotify** — delegates to receiveApprise (401)
+- **saveConfig** — error handling, invalid config (400), success with auth_tokens (200)
+- **saveBotPassword** — invalid password (400), valid password (200)
+- **getRooms** — empty rooms, room list with configured flag, exception → 500
+- **debug** — disabled (403), enabled for admin (200), enabled for non-admin (200)
+
+### `ImageCleanupTest.php`
+
+Unit tests for `Cron/ImageCleanup.php` cron job. Tests the full run() flow including early-exit paths and success logging.
+
+**Test groups:**
+
+- **Early exits** — no bot user, no images directory, root folder exception
+- **Success** — purge runs and logs count, no log when count is 0
+- **Edge cases** — null argument handling
+
+### `NavigationProviderTest.php`
+
+Unit tests for `NavigationProvider` settings link. Tests that the navigation link is only shown to admin users.
+
+**Test groups:**
+
+- **Non-admin** — null user, non-admin user → empty array
+- **Admin** — admin user → navigation link with correct metadata
+
+### `DebugToggleTest.php`
+
+Unit tests for `Command/DebugToggle.php` OCC command. Tests --status, --enable, --disable, toggle, and --enable/--disable conflict.
+
+**Test groups:**
+
+- **--status** — disabled by default, enabled when set
+- **--enable** — sets value to true, logs warning
+- **--disable** — sets value to false, logs success
+- **Toggle** — enables when disabled, disables when enabled
+- **Conflict** — --enable + --disable together returns INVALID (1)
+
+## Adding New Tests
+
+1. Determine which service or controller the new code belongs to.
+2. Add test methods to the appropriate test file.
+3. Use `makeTalkServiceMock()` (WebhookControllerTest) or the helper methods in TalkServiceTest to set up mocks.
+4. Run `composer test` to verify.
+
+## Test Architecture
+
+- **TalkService dependencies**: All 17 constructor parameters are mocked using PHPUnit's `getMockForTrait()` for abstract/interface types and `createMock()` for concrete classes.
+- **WebhookController dependencies**: TalkService is mocked; the other 9 dependencies use `createMock()`.
+- **ImageCleanup dependencies**: TalkService, IRootFolder, IUserManager, LoggerInterface — all mocked.
+- **NavigationProvider dependencies**: IURLGenerator, IUserSession, IConfig, IL10N — all mocked.
+- **DebugToggle dependencies**: IAppConfig — mocked; Symfony Console Input/Output used for CLI interaction.
+- **No real Nextcloud instance**: Tests verify business logic in isolation. Image upload/download tests verify the download logic but not real file storage.
+- **php://input**: The controller reads from `php://input` which cannot be mocked directly. Tests cover:
+  - Auth-failure path (no input needed)
+  - `$_GET` fallback for receive (simulated via `$_GET` in test setup)
+  - `$_POST` fallback for receiveApprise (simulated via `$_POST` in test setup)
+  - Payload parsing / mapping logic is covered by TalkServiceTest.
+
+## CI
+
+Tests run automatically on every push and PR via Gitea Actions. See `.gitea/workflows/ci.yml`.
+
+## Test Summary
+
+| File | Tests | Coverage |
+|------|-------|----------|
+| TalkServiceTest.php | 48 | All TalkService methods |
+| WebhookControllerTest.php | 21 | All controller endpoints + fallbacks |
+| ImageCleanupTest.php | 6 | All run() paths |
+| NavigationProviderTest.php | 3 | Admin/non-admin navigation |
+| DebugToggleTest.php | 7 | --status, --enable, --disable, toggle, conflict |
+| **Total** | **85** | All lib/ components covered |