Feature: Add message archiving system with browse-by-date selector

Implements automatic daily archiving of messages to improve performance
and enable browsing historical chat by date.

Backend changes:
- Add APScheduler for daily archiving at midnight (00:00 UTC)
- Create app/archiver/manager.py with archive logic and scheduler
- Extend parser.py to read from archive files and filter by days
- Add archive configuration to config.py (MC_ARCHIVE_*)

API changes:
- Extend GET /api/messages with archive_date and days parameters
- Add GET /api/archives endpoint to list available archives
- Add POST /api/archive/trigger for manual archiving

Frontend changes:
- Add date selector dropdown in navbar for archive browsing
- Implement archive list loading and date selection
- Update formatTime() to show full dates in archive view
- Live view now shows only last 7 days (configurable)

Docker & Config:
- Add archive volume mount in docker-compose.yml
- Add MC_ARCHIVE_DIR, MC_ARCHIVE_ENABLED, MC_ARCHIVE_RETENTION_DAYS env vars
- Update .env.example with archive configuration section

Documentation:
- Update README.md with archive feature and usage instructions
- Update .claude/instructions.md with archive endpoints

Key features:
- Automatic daily archiving (midnight UTC)
- Live view filtered to last 7 days for better performance
- Browse historical messages by date via dropdown selector
- Archives stored as dated files: {device}.YYYY-MM-DD.msgs
- Original .msgs file never modified (safe, read-only approach)

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.env.example

@@ -25,6 +25,19 @@ MC_REFRESH_INTERVAL=60
 # Hours of inactivity before contacts can be cleaned up
 MC_INACTIVE_HOURS=48
 
+# ============================================
+# Archive Configuration
+# ============================================
+
+# Directory for storing archived messages
+MC_ARCHIVE_DIR=/mnt/archive/meshcore
+
+# Enable automatic daily archiving at midnight
+MC_ARCHIVE_ENABLED=true
+
+# Number of days to show in live view (older messages available in archives)
+MC_ARCHIVE_RETENTION_DAYS=7
+
 # ============================================
 # Flask Server Configuration
 # ============================================