i think i got step one working

backend/dev_main.py

@@ -0,0 +1,94 @@
+"""Lightweight development backend for UI work.
+
+This avoids importing heavy ML dependencies so the UI can run during frontend
+development without installing large Python packages (torch/whisperx/etc.).
+Use this when you only need the health/file streaming endpoints.
+"""
+from fastapi import FastAPI, Request, HTTPException
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import StreamingResponse
+from pathlib import Path
+
+app = FastAPI(title="TalkEdit Dev Backend", version="0.0.1")
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+    expose_headers=["Content-Range", "Accept-Ranges", "Content-Length"],
+)
+
+
+MIME_MAP = {
+    ".mp4": "video/mp4",
+    ".mkv": "video/x-matroska",
+    ".mov": "video/quicktime",
+    ".avi": "video/x-msvideo",
+    ".webm": "video/webm",
+    ".m4a": "audio/mp4",
+    ".wav": "audio/wav",
+    ".mp3": "audio/mpeg",
+    ".flac": "audio/flac",
+}
+
+
+@app.get("/health")
+async def health():
+    return {"status": "ok"}
+
+
+@app.get("/file")
+async def serve_local_file(request: Request, path: str):
+    file_path = Path(path)
+    if not file_path.is_file():
+        raise HTTPException(status_code=404, detail=f"File not found: {path}")
+
+    file_size = file_path.stat().st_size
+    content_type = MIME_MAP.get(file_path.suffix.lower(), "application/octet-stream")
+
+    range_header = request.headers.get("range")
+    if range_header:
+        range_spec = range_header.replace("bytes=", "")
+        start_str, end_str = range_spec.split("-")
+        start = int(start_str) if start_str else 0
+        end = int(end_str) if end_str else file_size - 1
+        end = min(end, file_size - 1)
+        content_length = end - start + 1
+
+        def iter_range():
+            with open(file_path, "rb") as f:
+                f.seek(start)
+                remaining = content_length
+                while remaining > 0:
+                    chunk = f.read(min(65536, remaining))
+                    if not chunk:
+                        break
+                    remaining -= len(chunk)
+                    yield chunk
+
+        return StreamingResponse(
+            iter_range(),
+            status_code=206,
+            media_type=content_type,
+            headers={
+                "Content-Range": f"bytes {start}-{end}/{file_size}",
+                "Accept-Ranges": "bytes",
+                "Content-Length": str(content_length),
+            },
+        )
+
+    def iter_file():
+        with open(file_path, "rb") as f:
+            while chunk := f.read(65536):
+                yield chunk
+
+    return StreamingResponse(
+        iter_file(),
+        media_type=content_type,
+        headers={
+            "Accept-Ranges": "bytes",
+            "Content-Length": str(file_size),
+        },
+    )