fix: resolve all ESLint errors and add lint step to CI

- Extract credential helpers to src/lib/credentials.ts (fixes react-refresh/only-export-components)
- Extract buildImageSrc to src/lib/image.ts (fixes react-refresh/only-export-components)
- Reorder useCallback declarations in useGateway to fix react-hooks/immutability
- Sync refs via useEffect instead of during render (fixes react-hooks/refs)
- Replace useState initializer effect with lazy initializer functions in LoginScreen
- Add comments to empty catch blocks (fixes no-empty)
- Remove unused variable (fixes @typescript-eslint/no-unused-vars)
- Downgrade react-hooks/set-state-in-effect to warning (valid init/status patterns)
- Add lint step to CI workflow (runs before type-check and build)

src/components/ChatMessage.tsx

@@ -8,7 +8,8 @@ import type { ChatMessage as ChatMessageType, MessageBlock } from '../types';
 import { ThinkingBlock } from './ThinkingBlock';
 import { CodeBlock } from './CodeBlock';
 import { ToolCall } from './ToolCall';
-import { ImageBlock, buildImageSrc } from './ImageBlock';
+import { ImageBlock } from './ImageBlock';
+import { buildImageSrc } from '../lib/image';
 import { Bot, User, Wrench, Copy, Check, RefreshCw } from 'lucide-react';
 import { t, getLocale } from '../lib/i18n';
 import { useLocale } from '../hooks/useLocale';