fix: URL-decode DAV paths with spaces + feat: app passwords for Basic Auth

Bug fix:
- URL-decode paths in extract_webdav_path(), extract_caldav_path(),
  extract_carddav_path() so folders with spaces (e.g. 'My Folder') no
  longer return 404 when accessed via encoded URIs (%20)
- Properly encode href values in PROPFIND/PROPPATCH/LOCK XML responses
- Decode Destination header in MOVE/COPY operations

New feature - App Passwords (API keys for DAV clients):
- POST /api/auth/app-passwords  → create (shows token once)
- GET  /api/auth/app-passwords  → list (prefix only)
- DELETE /api/auth/app-passwords/:id → revoke
- Auth middleware now accepts both Bearer JWT and Basic Auth
- Argon2 hashed, scoped (webdav/caldav/carddav), optional expiry
- Compatible with DAVx5, Thunderbird, rclone, curl

Tested: 12/12 E2E tests pass (create, list, WebDAV/CalDAV/CardDAV
Basic Auth, URL-decode with spaces, wrong password 401, revoke, post-
revoke 401).

src/application/services/mod.rs

@@ -1,4 +1,5 @@
 pub mod admin_settings_service;
+pub mod app_password_service;
 pub mod auth_application_service;
 pub mod batch_operations;
 pub mod calendar_service;