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/config/index.md

@@ -0,0 +1,21 @@
+# Configuration
+
+OxiCloud is configured entirely via **environment variables** (no config files needed).
+
+## Sections
+
+- [Deployment & Docker](/config/deployment) — Docker Compose, Kubernetes Helm chart, image details
+- [Environment Variables](/config/env) — complete reference of all `OXICLOUD_*` variables
+- [OIDC / SSO](/config/oidc) — single sign-on with Keycloak, Authentik, Authelia, Google, Azure AD
+- [WOPI (Office Editing)](/config/wopi) — Collabora Online / OnlyOffice integration
+
+## Minimal `.env`
+
+```bash
+OXICLOUD_DB_CONNECTION_STRING=postgres://postgres:postgres@postgres:5432/oxicloud
+OXICLOUD_STORAGE_PATH=/app/storage
+OXICLOUD_SERVER_HOST=0.0.0.0
+OXICLOUD_SERVER_PORT=8086
+```
+
+That's enough to get started. All other settings have sensible defaults.