feat: add VitePress docs site, music file picker modal, Dockerfile optimization, i18n keys for 14 locales

- Add docs/ with VitePress site (19 pages): guide, config, architecture, FAQ
- Add GitHub Actions workflow for auto-deploy to GitHub Pages
- Replace music 'Add Tracks' upload picker with in-app audio file browser modal
- Add music picker CSS styles with dark theme support
- Add missing i18n keys (search_audio, no_audio_files, etc.) to all 14 locales
- Optimize Dockerfile: shared base stage, COPY --chmod, consolidated RUN, HEALTHCHECK
- Improve README: docs links, updated stats (222+ tests, 14 languages), feature status

docs/guide/caldav-carddav.md

@@ -0,0 +1,70 @@
+# CalDAV & CardDAV
+
+OxiCloud provides built-in CalDAV (calendar) and CardDAV (contacts) servers — no extra apps or plugins needed.
+
+## CalDAV (Calendars)
+
+### Endpoint
+
+```
+https://your-server:8086/caldav/
+```
+
+### Protocol Compliance
+
+- RFC 4791 (Calendar Access)
+- RFC 5545 (iCalendar format)
+- DAV capabilities: `1, 2, calendar-access`
+
+### Client Setup
+
+| Client | URL |
+|--------|-----|
+| Thunderbird | `https://your-server:8086/caldav/` |
+| GNOME Calendar | `https://your-server:8086/caldav/` |
+| Apple Calendar (macOS/iOS) | `https://your-server:8086/caldav/` |
+| DAVx⁵ (Android) | `https://your-server:8086/` (auto-discovery) |
+
+### Thunderbird Setup
+
+1. Open Thunderbird → **Calendar** tab
+2. Right-click → **New Calendar** → **On the Network**
+3. Format: **CalDAV**
+4. URL: `https://your-server:8086/caldav/`
+5. Enter your OxiCloud credentials
+
+---
+
+## CardDAV (Contacts)
+
+### Endpoint
+
+```
+https://your-server:8086/carddav/
+```
+
+### Protocol Compliance
+
+- RFC 6352 (CardDAV)
+- RFC 6350 (vCard 4.0)
+
+### Client Setup
+
+| Client | URL |
+|--------|-----|
+| Thunderbird | `https://your-server:8086/carddav/` |
+| GNOME Contacts | `https://your-server:8086/carddav/` |
+| Apple Contacts (macOS/iOS) | `https://your-server:8086/carddav/` |
+| DAVx⁵ (Android) | `https://your-server:8086/` (auto-discovery) |
+
+### DAVx⁵ (Android) Setup
+
+1. Install [DAVx⁵](https://www.davx5.com/) from F-Droid or Play Store
+2. Add account → **Login with URL and user name**
+3. Base URL: `https://your-server:8086/`
+4. Enter your OxiCloud credentials
+5. DAVx⁵ auto-discovers both CalDAV and CardDAV endpoints
+
+::: info
+DAVx⁵ file sync works. CalDAV/CardDAV support on DAVx⁵ is still being refined.
+:::