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/services/transcribe.py

@@ -0,0 +1,46 @@
+"""Stub for the transcribe + summarize pipeline.
+
+This module is intentionally a placeholder for A3. The real implementation
+lands in A5 and will:
+  1. Download the object from MinIO
+  2. Probe duration and size
+  3. If file > 24 MB, ffmpeg silencedetect → split into <20 MB chunks
+  4. Call Groq Whisper for each chunk, shift timestamps, merge
+  5. Call Poe Claude with map-reduce for long audio
+  6. Persist segments + summary, update meeting.status to done
+"""
+
+import asyncio
+from sqlmodel import select
+from ..db import AsyncSessionLocal
+from ..models import Meeting, MeetingStatus
+
+
+async def process_meeting(meeting_id: int) -> None:
+    """Background task launched after upload-complete.
+
+    For A3 we just walk the state machine so the frontend can see status
+    transitions; A5 swaps in real Groq/Poe calls.
+    """
+    async with AsyncSessionLocal() as session:
+        meeting = await session.get(Meeting, meeting_id)
+        if not meeting:
+            return
+
+        try:
+            for status, delay in [
+                (MeetingStatus.splitting, 1),
+                (MeetingStatus.transcribing, 2),
+                (MeetingStatus.summarizing, 1),
+                (MeetingStatus.done, 0),
+            ]:
+                meeting.status = status
+                if status == MeetingStatus.transcribing:
+                    meeting.chunks_total = 1
+                    meeting.chunks_done = 1
+                await session.commit()
+                await asyncio.sleep(delay)
+        except Exception as exc:
+            meeting.status = MeetingStatus.failed
+            meeting.error = str(exc)
+            await session.commit()