extract routes from main.py into domain routers (Phase 4)

Split the 2,578-line main.py (90 routes) into 12 domain-specific router
modules under routes/. main.py is now a 45-line entry point.

New structure:
- app.py: FastAPI instance, CORS, startup/shutdown, safe_content_disposition
- routes/: health, profiles, channels, generations, history, transcription,
  stories, effects, audio, models, tasks, cuda
- services/cuda.py: moved from cuda_download.py

Also includes Phase 5 database/ package (from parallel agent):
- database/__init__.py re-exports all symbols for backward compat
- database/models.py, session.py, migrations.py, seed.py

All 90 routes verified registered and app imports cleanly.

backend/routes/history.py

@@ -0,0 +1,174 @@
+"""Generation history endpoints."""
+
+import io
+from pathlib import Path
+
+from fastapi import APIRouter, Depends, File, HTTPException, UploadFile
+from fastapi.responses import FileResponse, StreamingResponse
+from sqlalchemy.orm import Session
+
+from .. import export_import, history, models
+from ..app import safe_content_disposition
+from ..database import Generation as DBGeneration, VoiceProfile as DBVoiceProfile, get_db
+
+router = APIRouter()
+
+
+@router.get("/history", response_model=models.HistoryListResponse)
+async def list_history(
+    profile_id: str | None = None,
+    search: str | None = None,
+    limit: int = 50,
+    offset: int = 0,
+    db: Session = Depends(get_db),
+):
+    """List generation history with optional filters."""
+    query = models.HistoryQuery(
+        profile_id=profile_id,
+        search=search,
+        limit=limit,
+        offset=offset,
+    )
+    return await history.list_generations(query, db)
+
+
+@router.get("/history/stats")
+async def get_stats(db: Session = Depends(get_db)):
+    """Get generation statistics."""
+    return await history.get_generation_stats(db)
+
+
+@router.post("/history/import")
+async def import_generation(
+    file: UploadFile = File(...),
+    db: Session = Depends(get_db),
+):
+    """Import a generation from a ZIP archive."""
+    MAX_FILE_SIZE = 50 * 1024 * 1024
+
+    content = await file.read()
+
+    if len(content) > MAX_FILE_SIZE:
+        raise HTTPException(
+            status_code=400, detail=f"File too large. Maximum size is {MAX_FILE_SIZE / (1024 * 1024)}MB"
+        )
+
+    try:
+        result = await export_import.import_generation_from_zip(content, db)
+        return result
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
+
+
+@router.get("/history/{generation_id}", response_model=models.HistoryResponse)
+async def get_generation(
+    generation_id: str,
+    db: Session = Depends(get_db),
+):
+    """Get a generation by ID."""
+    result = (
+        db.query(DBGeneration, DBVoiceProfile.name.label("profile_name"))
+        .join(DBVoiceProfile, DBGeneration.profile_id == DBVoiceProfile.id)
+        .filter(DBGeneration.id == generation_id)
+        .first()
+    )
+
+    if not result:
+        raise HTTPException(status_code=404, detail="Generation not found")
+
+    gen, profile_name = result
+    return models.HistoryResponse(
+        id=gen.id,
+        profile_id=gen.profile_id,
+        profile_name=profile_name,
+        text=gen.text,
+        language=gen.language,
+        audio_path=gen.audio_path,
+        duration=gen.duration,
+        seed=gen.seed,
+        instruct=gen.instruct,
+        created_at=gen.created_at,
+    )
+
+
+@router.post("/history/{generation_id}/favorite")
+async def toggle_favorite(
+    generation_id: str,
+    db: Session = Depends(get_db),
+):
+    """Toggle the favorite status of a generation."""
+    gen = db.query(DBGeneration).filter_by(id=generation_id).first()
+    if not gen:
+        raise HTTPException(status_code=404, detail="Generation not found")
+    gen.is_favorited = not gen.is_favorited
+    db.commit()
+    return {"is_favorited": gen.is_favorited}
+
+
+@router.delete("/history/{generation_id}")
+async def delete_generation(
+    generation_id: str,
+    db: Session = Depends(get_db),
+):
+    """Delete a generation."""
+    success = await history.delete_generation(generation_id, db)
+    if not success:
+        raise HTTPException(status_code=404, detail="Generation not found")
+    return {"message": "Generation deleted successfully"}
+
+
+@router.get("/history/{generation_id}/export")
+async def export_generation(
+    generation_id: str,
+    db: Session = Depends(get_db),
+):
+    """Export a generation as a ZIP archive."""
+    try:
+        generation = db.query(DBGeneration).filter_by(id=generation_id).first()
+        if not generation:
+            raise HTTPException(status_code=404, detail="Generation not found")
+
+        zip_bytes = export_import.export_generation_to_zip(generation_id, db)
+
+        safe_text = "".join(c for c in generation.text[:30] if c.isalnum() or c in (" ", "-", "_")).strip()
+        if not safe_text:
+            safe_text = "generation"
+        filename = f"generation-{safe_text}.voicebox.zip"
+
+        return StreamingResponse(
+            io.BytesIO(zip_bytes),
+            media_type="application/zip",
+            headers={"Content-Disposition": safe_content_disposition("attachment", filename)},
+        )
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=str(e))
+
+
+@router.get("/history/{generation_id}/export-audio")
+async def export_generation_audio(
+    generation_id: str,
+    db: Session = Depends(get_db),
+):
+    """Export only the audio file from a generation."""
+    generation = db.query(DBGeneration).filter_by(id=generation_id).first()
+    if not generation:
+        raise HTTPException(status_code=404, detail="Generation not found")
+
+    audio_path = Path(generation.audio_path)
+    if not audio_path.exists():
+        raise HTTPException(status_code=404, detail="Audio file not found")
+
+    safe_text = "".join(c for c in generation.text[:30] if c.isalnum() or c in (" ", "-", "_")).strip()
+    if not safe_text:
+        safe_text = "generation"
+    filename = f"{safe_text}.wav"
+
+    return FileResponse(
+        audio_path,
+        media_type="audio/wav",
+        headers={"Content-Disposition": safe_content_disposition("attachment", filename)},
+    )