fix: Complete Issue #72 - Fix automatic mirroring and repository cleanup

Major fixes for Docker environment variable issues and cleanup functionality:

🔧 **Duration Parser & Scheduler Fixes**
- Add comprehensive duration parser supporting "8h", "30m", "24h" formats
- Fix GITEA_MIRROR_INTERVAL environment variable mapping to scheduler
- Auto-enable scheduler when GITEA_MIRROR_INTERVAL is set
- Improve scheduler logging to clarify timing behavior (from last run, not startup)

🧹 **Repository Cleanup Service**
- Complete repository cleanup service for orphaned repos (unstarred, deleted)
- Fix cleanup configuration logic - now works with CLEANUP_DELETE_IF_NOT_IN_GITHUB=true
- Auto-enable cleanup when deleteIfNotInGitHub is enabled
- Add manual cleanup trigger API endpoint (/api/cleanup/trigger)
- Support archive/delete actions with dry-run mode and protected repos

🐛 **Environment Variable Integration**
- Fix scheduler not recognizing GITEA_MIRROR_INTERVAL=8h
- Fix cleanup requiring both CLEANUP_DELETE_FROM_GITEA and CLEANUP_DELETE_IF_NOT_IN_GITHUB
- Auto-enable services when relevant environment variables are set
- Better error logging and debugging information

📚 **Documentation Updates**
- Update .env.example with auto-enabling behavior notes
- Update ENVIRONMENT_VARIABLES.md with clarified functionality
- Add comprehensive tests for duration parsing

This resolves the core issues where:
1. GITEA_MIRROR_INTERVAL=8h was not working for automatic mirroring
2. Repository cleanup was not working despite CLEANUP_DELETE_IF_NOT_IN_GITHUB=true
3. Users had no visibility into why scheduling/cleanup wasn't working

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

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

src/lib/env-config-loader.ts

@@ -135,8 +135,11 @@ function parseEnvConfig(): EnvConfig {
       mirrorMetadata: process.env.MIRROR_METADATA === 'true',
     },
     schedule: {
-      enabled: process.env.SCHEDULE_ENABLED === 'true',
-      interval: process.env.SCHEDULE_INTERVAL || process.env.DELAY, // Support both old DELAY and new SCHEDULE_INTERVAL
+      enabled: process.env.SCHEDULE_ENABLED === 'true' || 
+               !!process.env.GITEA_MIRROR_INTERVAL || 
+               !!process.env.SCHEDULE_INTERVAL || 
+               !!process.env.DELAY, // Auto-enable if any interval is specified
+      interval: process.env.SCHEDULE_INTERVAL || process.env.GITEA_MIRROR_INTERVAL || process.env.DELAY, // Support GITEA_MIRROR_INTERVAL, SCHEDULE_INTERVAL, and old DELAY
       concurrent: process.env.SCHEDULE_CONCURRENT === 'true',
       batchSize: process.env.SCHEDULE_BATCH_SIZE ? parseInt(process.env.SCHEDULE_BATCH_SIZE, 10) : undefined,
       pauseBetweenBatches: process.env.SCHEDULE_PAUSE_BETWEEN_BATCHES ? parseInt(process.env.SCHEDULE_PAUSE_BETWEEN_BATCHES, 10) : undefined,
@@ -155,7 +158,8 @@ function parseEnvConfig(): EnvConfig {
       recentThreshold: process.env.SCHEDULE_RECENT_THRESHOLD ? parseInt(process.env.SCHEDULE_RECENT_THRESHOLD, 10) : undefined,
     },
     cleanup: {
-      enabled: process.env.CLEANUP_ENABLED === 'true',
+      enabled: process.env.CLEANUP_ENABLED === 'true' || 
+               process.env.CLEANUP_DELETE_IF_NOT_IN_GITHUB === 'true', // Auto-enable if deleteIfNotInGitHub is enabled
       retentionDays: process.env.CLEANUP_RETENTION_DAYS ? parseInt(process.env.CLEANUP_RETENTION_DAYS, 10) : undefined,
       deleteFromGitea: process.env.CLEANUP_DELETE_FROM_GITEA === 'true',
       deleteIfNotInGitHub: process.env.CLEANUP_DELETE_IF_NOT_IN_GITHUB === 'true',