docs: media player subsystem architecture and conventions

Document the media server process, /media/ port map, library layout on
the ./media bind mount, Hope's media MCP toolset, the music/mic
mutual-exclusion rule, and yt-dlp download/proxy conventions.

web/media_server.py

@@ -63,6 +63,12 @@ _executor = ThreadPoolExecutor(max_workers=1, thread_name_prefix="media-dl")
 
 for _d in (FILES_DIR, THUMBS_DIR, JOBS_DIR):
     _d.mkdir(parents=True, exist_ok=True)
+    # The bind mount may be inspected/cleaned from the host by a non-root
+    # user (Unraid share convention) — keep the dirs world-traversable.
+    try:
+        os.chmod(_d, 0o777)
+    except OSError:
+        pass
 
 
 # ── Library store ───────────────────────────────────────────────────────────
@@ -263,6 +269,7 @@ def _download_worker(job: dict, track: dict, video_id: str) -> None:
         for line in proc.stdout:
             if time.monotonic() > deadline:
                 proc.kill()
+                proc.wait(timeout=30)
                 raise RuntimeError(f"Download exceeded {DOWNLOAD_TIMEOUT}s")
             line = line.strip()
             m = _PROGRESS_RE.search(line)
@@ -385,7 +392,10 @@ async def search(request: Request) -> dict:
     query = str(body.get("query", "")).strip()
     if not query:
         raise HTTPException(400, "query is required")
-    limit = max(1, min(int(body.get("limit", 6)), 15))
+    try:
+        limit = max(1, min(int(body.get("limit", 6)), 15))
+    except (TypeError, ValueError):
+        raise HTTPException(400, "limit must be an integer")
     return {"query": query, "results": _run_search(query, limit)}
 
 
@@ -479,10 +489,11 @@ async def control(request: Request) -> dict:
         elif action == "stop":
             st["desired"] = "stopped"
         elif action == "seek":
-            st["seek_hint"] = {
-                "position": max(0.0, float(body.get("position", 0))),
-                "ts": time.time(),
-            }
+            try:
+                position = max(0.0, float(body.get("position", 0)))
+            except (TypeError, ValueError):
+                raise HTTPException(400, "position must be a number")
+            st["seek_hint"] = {"position": position, "ts": time.time()}
         elif action == "skip":
             current = st["track_id"]
             candidates = sorted(
@@ -574,7 +585,7 @@ async def stream_proxy(track_id: str, request: Request):
         raise HTTPException(409, f"track is {track.get('status')}, not ready")
 
     range_header = request.headers.get("range")
-    headers = {"Range": range_header} if range_header else {"Range": "bytes=0-"}
+    headers = {"Range": range_header} if range_header else {}
     client = httpx.AsyncClient(timeout=httpx.Timeout(30, read=600), follow_redirects=True)
     try:
         upstream = await client.send(client.build_request("GET", track["url"], headers=headers), stream=True)