Enhance error handling and validation in agents and routes

- Added logging for empty responses in GeminiAgent and OpenRouterAgent to track potential session context issues.
- Refactored settings file path usage in OpenRouterAgent to use a constant for better maintainability.
- Improved error handling in SessionRoutes to log generator failures with detailed context.
- Implemented JSON parsing error handling in SettingsRoutes to manage corrupted settings files gracefully.
- Added validation for CLAUDE_MEM_OPENROUTER_MAX_CONTEXT_MESSAGES, CLAUDE_MEM_OPENROUTER_MAX_TOKENS, and CLAUDE_MEM_OPENROUTER_SITE_URL in SettingsRoutes to ensure valid configuration.

src/services/worker/http/routes/SessionRoutes.ts

@@ -135,6 +135,13 @@ export class SessionRoutes extends BaseRouteHandler {
     session.currentProvider = provider;
 
     session.generatorPromise = agent.startSession(session, this.workerService)
+      .catch(error => {
+        logger.error('SESSION', `Generator failed`, {
+          sessionId: session.sessionDbId,
+          provider: provider,
+          error: error.message
+        }, error);
+      })
       .finally(() => {
         logger.info('SESSION', `Generator finished`, { sessionId: session.sessionDbId });
         session.generatorPromise = null;