Initial commit: scan_web integrated recording UI

FastAPI backend + vanilla JS frontend for LiDAR/camera startup, camera
settings, and rosbag recording, unifying the previous scan_gui/scan_gui_dual/
scan_gui_triple desktop tools into one web app.

backend/routers/telemetry.py

@@ -0,0 +1,74 @@
+from __future__ import annotations
+
+import asyncio
+
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+
+import config
+from log_tail import LogTailer
+from routers.system import build_status
+
+router = APIRouter()
+
+STATUS_PUSH_HZ = 1.0  # slowed from 2.0 — paired with health.py's wider RATE_WINDOW,
+                      # the operator asked for a calmer/more trustworthy number over a
+                      # snappier one (2026-08-06).
+LOG_POLL_HZ = 4.0
+
+
+@router.websocket("/ws/status")
+async def ws_status(ws: WebSocket):
+    await ws.accept()
+    period = 1.0 / STATUS_PUSH_HZ
+    try:
+        while True:
+            await ws.send_json(build_status(ws.app))
+            await asyncio.sleep(period)
+    except WebSocketDisconnect:
+        pass
+
+
+@router.websocket("/ws/pointcloud")
+async def ws_pointcloud(ws: WebSocket, profile: str = "desktop"):
+    """M3 live scan view — binary-framed decimated point cloud, see
+    pointcloud_codec.py for the wire format. `profile` picks desktop vs.
+    phone point/Hz budgets rather than trusting client-supplied numbers
+    directly (a client could otherwise ask for an unbounded frame size)."""
+    await ws.accept()
+    prof = config.POINTCLOUD_PROFILES.get(profile, config.POINTCLOUD_PROFILES["desktop"])
+    period = 1.0 / prof["hz"]
+    ros = ws.app.state.ros
+    try:
+        while True:
+            await ws.send_bytes(ros.pointcloud.encode_frame(max_points=prof["max_points"]))
+            await asyncio.sleep(period)
+    except WebSocketDisconnect:
+        pass
+
+
+@router.websocket("/ws/logs")
+async def ws_logs(ws: WebSocket):
+    """Unified log tail — mirrors the old PyQt GUIs' single scrollback pane.
+    Sends recent backlog once on connect, then only newly-appended lines."""
+    await ws.accept()
+    tailer = LogTailer({
+        "lidar": config.LIDAR_LOG_PATH,
+        "camera": config.CAMERA_LOG_PATH,
+        "recording": config.RECORDING_LOG_PATH,
+        "fastlio": config.FASTLIO_LOG_PATH,
+    })
+    backlog = []
+    for tag in ("lidar", "camera", "recording", "fastlio"):
+        backlog += [{"tag": tag, "line": ln} for ln in tailer.read_tail(tag, max_lines=80)]
+    if backlog:
+        await ws.send_json({"backlog": backlog})
+
+    period = 1.0 / LOG_POLL_HZ
+    try:
+        while True:
+            new_lines = [{"tag": tag, "line": line} for tag, line in tailer.read_new()]
+            if new_lines:
+                await ws.send_json({"lines": new_lines})
+            await asyncio.sleep(period)
+    except WebSocketDisconnect:
+        pass