feat: add PairDrop file sharing service (drop.pivoine.art)

Added PairDrop stack for peer-to-peer file sharing:
- WebRTC-based direct file transfers between devices
- No file size limits or server storage
- End-to-end encrypted transfers
- Local network auto-discovery
- Cross-platform support (desktop, mobile, tablets)
- Progressive Web App installable on mobile
- Rate limiting enabled for security

PairDrop provides secure, private file sharing without uploading
files to any server - all transfers happen directly between devices.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CLAUDE.md

@@ -25,6 +25,7 @@ Root `compose.yaml` uses Docker Compose's `include` directive to orchestrate mul
 - **vert**: VERT file format converter (WebAssembly-based, stateless)
 - **paint**: miniPaint web-based image editor (built from GitHub)
 - **jelly**: Jellyfin media server with hardware transcoding
+- **drop**: PairDrop peer-to-peer file sharing
 - **restic**: Backrest backup system with restic backend
 - **sablier**: Dynamic scaling plugin for Traefik
 - **vpn**: WireGuard VPN (wg-easy)
@@ -322,6 +323,33 @@ Access https://jelly.pivoine.art to browse and stream your media. Jellyfin will
 
 **Note**: Jellyfin requires the HiDrive WebDAV mount to be active on the host at `/mnt/hidrive`.
 
+### PairDrop (drop/compose.yaml)
+PairDrop peer-to-peer file sharing service:
+- **pairdrop**: PairDrop app exposed at `drop.pivoine.art:3000`
+  - Local network file sharing between devices
+  - Peer-to-peer file transfer via WebRTC
+  - No file size limits
+  - Works across platforms (desktop, mobile, tablets)
+  - End-to-end encrypted transfers
+  - No file uploads to server (direct peer connections)
+  - Rate limiting enabled for security
+  - Stateless architecture (no data persistence)
+
+**Features**:
+- Share files by opening the same URL on multiple devices
+- Devices on the same network automatically discover each other
+- Works across different networks via public room codes
+- Text messages and file sharing support
+- Progressive Web App (PWA) installable on mobile
+
+**Usage**:
+1. Open https://drop.pivoine.art on your device
+2. Open the same URL on another device
+3. Devices will appear and you can share files directly
+4. Files transfer peer-to-peer without uploading to server
+
+**Note**: PairDrop is stateless and doesn't require backups as no data is persisted. All transfers happen directly between devices.
+
 ### Restic (restic/compose.yaml)
 Backrest backup system with restic backend:
 - **backrest**: Backrest web UI exposed at `restic.pivoine.art:9898`