feat(health): optimize validation, add automatic metadata regeneration and enforce strict linking

[drondeseries]

Summary

This PR introduces several critical improvements to the health monitoring and repair system to prevent stalling, reduce bandwidth usage, and automate the recovery of physically corrupted metadata.

🚀 Key Features & Fixes

1. Optimized Usenet Validation (Bandwidth & Speed)

   • Issue: Health checks were downloading full segments even after confirmation, leading to high bandwidth usage (73GB+) and worker stalls.
   • Fix: Modified validation logic to immediately cancel the segment download as soon as the first non-zero byte is detected.
   • Result: Health check cycles now complete in under 1 minute with minimal data usage.

2. Automatic Metadata Regeneration

   • New Feature: Added which automatically searches the persistent .nzbs folder when a file has corrupted metadata and no library path.
   • Benefit: Allows the system to "self-heal" by rebuilding the .meta file from the original NZB without requiring a redownload or ARR intervention.

3. Improved Corruption Handling in Library Sync

   • Issue: Files with physically corrupted metadata were ignored by the sync process and never reached the health database.
   • Fix: Updated LibrarySync to detect unmarshal errors and register them as corrupted entries in the database.
   • Result: Corrupted files are now automatically caught, hidden from the mount (moved to corrupted_metadata/), and queued for repair.

4. Strict ARR Linking

   • Removed legacy filename parsing fallbacks for Sonarr and Radarr. Repairs are now strictly triggered only when a direct path match or known relative path suffix is confirmed by the ARR instance, preventing "zombie" or incorrect repair triggers.

5. Configurable Health Timeouts

   • Added read_timeout_seconds to the health configuration (defaulting to 30s) to allow users to tune the system for slow Usenet providers.

🛠 Implementation Details

• Updated internal/usenet/validation.go with context cancellation logic.
• Extended internal/importer/service.go with NZB search and re-processing capabilities.
• Enhanced internal/database/health_repository.go query to pick up metadata-corrupted files even without a library_path.
• Wired importerService into HealthWorker via internal/health/worker.go and setup commands.