feat: Add Chat UX improvements with notifications and @mention support

- Add ActionBar component with expandable toolbar for mobile
- Add @mention functionality with autocomplete dropdown
- Add browser notification system (push, sound, vibration)
- Add NotificationSettings modal for user preferences
- Add mention badges on room list cards
- Add ReportPreview with Markdown rendering and copy/download
- Add message copy functionality with hover actions
- Add backend mentions field to messages with Alembic migration
- Add lots field to rooms, remove templates
- Optimize WebSocket database session handling
- Various UX polish (animations, accessibility)

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

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

app/modules/report_generation/router.py

@@ -7,6 +7,7 @@ FastAPI router with all report-related endpoints:
 - GET /api/rooms/{room_id}/reports/{report_id}/download - Download report .docx
 """
 import logging
+from urllib.parse import quote
 from fastapi import APIRouter, Depends, HTTPException, status, BackgroundTasks
 from fastapi.responses import StreamingResponse
 from sqlalchemy.orm import Session
@@ -64,6 +65,33 @@ async def _broadcast_report_progress(
     await ws_manager.broadcast_to_room(room_id, payload)
 
 router = APIRouter(prefix="/api/rooms/{room_id}/reports", tags=["Report Generation"])
+health_router = APIRouter(prefix="/api/reports", tags=["Report Generation"])
+
+
+@health_router.get("/health", response_model=schemas.HealthCheckResponse)
+async def check_dify_health():
+    """Check DIFY AI service connection status
+
+    Returns:
+        Health check result with status and message
+    """
+    if not settings.DIFY_API_KEY:
+        return schemas.HealthCheckResponse(
+            status="error",
+            message="DIFY_API_KEY 未設定，請聯繫系統管理員"
+        )
+
+    try:
+        result = await dify_service.test_connection()
+        return schemas.HealthCheckResponse(
+            status=result["status"],
+            message=result["message"]
+        )
+    except DifyAPIError as e:
+        return schemas.HealthCheckResponse(
+            status="error",
+            message=str(e)
+        )
 
 
 @router.post("/generate", response_model=schemas.ReportGenerateResponse, status_code=status.HTTP_202_ACCEPTED)
@@ -202,6 +230,75 @@ async def get_report_status(
     )
 
 
+@router.get("/{report_id}/markdown", response_model=schemas.ReportMarkdownResponse)
+async def get_report_markdown(
+    room_id: str,
+    report_id: str,
+    db: Session = Depends(get_db),
+    room_context: dict = Depends(require_room_member),
+):
+    """Get report content as Markdown for in-page preview
+
+    Args:
+        room_id: Room ID
+        report_id: Report ID to get markdown for
+
+    Returns:
+        Markdown formatted report content
+    """
+    report = (
+        db.query(GeneratedReport)
+        .filter(
+            GeneratedReport.report_id == report_id,
+            GeneratedReport.room_id == room_id,
+        )
+        .first()
+    )
+
+    if not report:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Report not found",
+        )
+
+    if report.status != ReportStatus.COMPLETED.value:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"Report is not ready. Status: {report.status}",
+        )
+
+    if not report.report_json:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Report content not found",
+        )
+
+    # Collect room data for markdown generation
+    data_service = ReportDataService(db)
+    room_data = data_service.collect_room_data(room_id)
+
+    if not room_data:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Room not found",
+        )
+
+    prompt_data = data_service.to_prompt_dict(room_data)
+
+    # Generate markdown
+    markdown_content = docx_service.to_markdown(
+        room_data=prompt_data["room_data"],
+        ai_content=report.report_json,
+        files=prompt_data["files"],
+    )
+
+    return schemas.ReportMarkdownResponse(
+        report_id=report.report_id,
+        report_title=report.report_title,
+        markdown=markdown_content,
+    )
+
+
 @router.get("/{report_id}/download")
 async def download_report(
     room_id: str,
@@ -262,11 +359,16 @@ async def download_report(
         filename = report.report_title or f"report_{report.report_id[:8]}"
         filename = f"{filename}.docx"
 
+        # Use RFC 5987 format for non-ASCII filenames
+        # Provide ASCII fallback for older clients + UTF-8 encoded version
+        ascii_filename = f"report_{report.report_id[:8]}.docx"
+        encoded_filename = quote(filename)
+
         return StreamingResponse(
             io.BytesIO(content),
             media_type="application/vnd.openxmlformats-officedocument.wordprocessingml.document",
             headers={
-                "Content-Disposition": f'attachment; filename="{filename}"',
+                "Content-Disposition": f"attachment; filename=\"{ascii_filename}\"; filename*=UTF-8''{encoded_filename}",
             },
         )