feat(api): A3 backend skeleton with FastAPI + SQLModel

- 3 tables: Meeting / TranscriptSegment / Summary (with state machine)
- Routes: /api/upload-url + /api/upload-complete + meetings CRUD
- MinIO presigned PUT for direct browser upload
- BackgroundTasks state-machine stub for A5 to flesh out
- SQLite for local dev, PostgreSQL+asyncpg for prod
- CORS configured for frontend on 4490

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/schemas.py

@@ -0,0 +1,38 @@
+from datetime import datetime
+from typing import Optional
+from pydantic import BaseModel
+from .models import MeetingStatus
+
+
+class UploadUrlRequest(BaseModel):
+    filename: str
+    content_type: str = "audio/mp4"
+    title: Optional[str] = None
+    participants: Optional[str] = None
+
+
+class UploadUrlResponse(BaseModel):
+    meeting_id: int
+    upload_url: str
+    object_key: str
+
+
+class UploadCompleteRequest(BaseModel):
+    meeting_id: int
+    file_size: int
+
+
+class MeetingRead(BaseModel):
+    id: int
+    title: str
+    participants: Optional[str] = None
+    duration: Optional[int] = None
+    file_size: Optional[int] = None
+    status: MeetingStatus
+    chunks_done: int
+    chunks_total: int
+    error: Optional[str] = None
+    created_at: datetime
+
+    class Config:
+        from_attributes = True