feat: v1.5.0 Phase 2 - Debug File Management

Implement debug file management system with configuration controls,
automatic cleanup, and security improvements per v1.5.0 Phase 2.

## Changes

### Configuration (config.py)
- Add DEBUG_SAVE_FAILED_UPLOADS (default: false, production-safe)
- Add DEBUG_FILE_MAX_AGE_DAYS (default: 7 days)
- Add DEBUG_FILE_MAX_SIZE_MB (default: 100MB)

### Media Validation (media.py)
- Check config before saving debug files
- Sanitize filenames to prevent path traversal
- Pattern: alphanumeric + "._-", truncated to 50 chars
- Add cleanup_old_debug_files() function
  * Age-based cleanup (delete files older than MAX_AGE)
  * Size-based cleanup (delete oldest if total > MAX_SIZE)

### Application Startup (__init__.py)
- Run cleanup_old_debug_files() on startup
- Automatic maintenance of debug directory

### Tests (test_debug_file_management.py)
- 15 comprehensive tests
- Config defaults and overrides
- Debug file saving behavior
- Filename sanitization security
- Cleanup age and size limits
- Startup integration

## Security Improvements
- Debug saving disabled by default (production-safe)
- Filename sanitization prevents path traversal
- Automatic cleanup prevents disk exhaustion

## Acceptance Criteria
- [x] Configuration options added
- [x] Debug saving disabled by default
- [x] Filename sanitized before saving
- [x] Cleanup runs on startup
- [x] Old files deleted based on age
- [x] Size limit enforced

All tests pass. Ready for architect review.

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

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

starpunk/config.py

@@ -97,6 +97,11 @@ def load_config(app, config_override=None):
     app.config["METRICS_BUFFER_SIZE"] = int(os.getenv("METRICS_BUFFER_SIZE", "1000"))
     app.config["METRICS_MEMORY_INTERVAL"] = int(os.getenv("METRICS_MEMORY_INTERVAL", "30"))
 
+    # Debug file configuration (v1.5.0 Phase 2)
+    app.config["DEBUG_SAVE_FAILED_UPLOADS"] = os.getenv("DEBUG_SAVE_FAILED_UPLOADS", "false").lower() == "true"
+    app.config["DEBUG_FILE_MAX_AGE_DAYS"] = int(os.getenv("DEBUG_FILE_MAX_AGE_DAYS", "7"))
+    app.config["DEBUG_FILE_MAX_SIZE_MB"] = int(os.getenv("DEBUG_FILE_MAX_SIZE_MB", "100"))
+
     # Apply overrides if provided
     if config_override:
         app.config.update(config_override)