fix: Multiple bug fixes and improvements

- Fix Invalid Date display in Dashboard notifications
- Fix timezone offset (8 hours) in Trading Records time display
- Fix position closing failures due to commission discrepancies (fetch actual exchange position size for reduce_only orders)
- Fix IBKR connection error 'no current event loop in thread' by ensuring asyncio event loop exists
- Fix duplicate orders on same candle by extending signal deduplication to close signals
- Add responsive design for Profile page (mobile-friendly)
- Remove unused strategy_code module and database table
- Fix LLM service to support multiple providers (OpenRouter, OpenAI, DeepSeek, Grok, Google)
- Add auto-detection of configured LLM provider based on API key availability
- Fix AI code generation to use unified LLMService with proper provider selection
- Fix crypto symbol format handling (ETH/USDT no longer becomes ETH/USDT/USDT)
- Fix Commission display showing '0E-8' in Trading Records
- Fix P&L display for signal-only trades (show '--' for unrealized P&L)
- Fix OAuth login not updating last_login_at for new users
- Add migration script for notification_settings column
- Update env.example with new LLM provider configurations
- Remove ESLint rule that was not defined in config

backend_api_python/migrations/add_notification_settings.sql

@@ -0,0 +1,16 @@
+-- Migration: Add notification_settings column to qd_users table
+-- Run this if you see error: column "notification_settings" does not exist
+
+-- Add notification_settings column (if not exists)
+DO $$ 
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM information_schema.columns 
+        WHERE table_name = 'qd_users' AND column_name = 'notification_settings'
+    ) THEN
+        ALTER TABLE qd_users ADD COLUMN notification_settings TEXT DEFAULT '';
+        RAISE NOTICE 'Column notification_settings added to qd_users';
+    ELSE
+        RAISE NOTICE 'Column notification_settings already exists';
+    END IF;
+END $$;