chore: remove unused code and suppress noisy Claude Code logs

- Delete unused files: retry.js, app-init.js, model-manager.js
- Remove duplicate error helpers from helpers.js (exist in errors.js)
- Remove unused exports from signature-cache.js, logger.js
- Remove unused frontend code: ErrorHandler methods, validators, canDelete, destroy
- Make internal functions private in thinking-utils.js
- Remove commented-out code from constants.js
- Remove deprecated .glass-panel CSS class
- Add silent handler for Claude Code event logging (/api/event_logging/batch)
- Suppress logging for /v1/messages/count_tokens (501 responses)
- Fix catch-all to use originalUrl (wildcard strips req.path)

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

src/utils/logger.js

@@ -140,6 +140,3 @@ class Logger extends EventEmitter {
 
 // Export a singleton instance
 export const logger = new Logger();
-
-// Export class if needed for multiple instances
-export { Logger };