feat: add compare endpoint to webui, fix duplicate Done. line

- Add /compare POST endpoint that runs the two-instance diff
- Add "Compare Instances" button to the dashboard
- Fix double "Done." output: the summary line was logged both as a
  regular log event and as the done event message

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

webui.py

@@ -258,9 +258,10 @@ async def run_sync_job(job_id: str, command: str) -> None:
         summary_line = ""
         async for raw in proc.stdout:
             text = raw.decode(errors="replace").rstrip()
-            _jobs[job_id]["output"].append({"type": "log", "message": text})
             if text.startswith("Done."):
                 summary_line = text
+            else:
+                _jobs[job_id]["output"].append({"type": "log", "message": text})
         await proc.wait()
         success = proc.returncode == 0
         _jobs[job_id]["output"].append({
@@ -514,6 +515,7 @@ async def dashboard():
     <button class="btn btn-primary" onclick="doSync('/pull','Pulling from Outline')">Get from Outline</button>
     <button class="btn btn-success" onclick="doSync('/push','Sending to Outline')"{push_dis}>{push_label}</button>
     <a href="/changes" class="btn btn-secondary">Preview Changes</a>
+    <button class="btn btn-secondary" onclick="doSync('/compare','Comparing instances')">Compare Instances</button>
   </div>
   <div id="output"></div>
 </div>
@@ -552,6 +554,21 @@ async def start_pull():
     return {"job_id": job_id, "stream_url": f"/stream/{job_id}"}
 
 
+@app.post("/compare")
+async def start_compare():
+    if _active_job is not None:
+        raise HTTPException(status_code=409, detail="A sync job is already running")
+    settings = _load_settings()
+    local = settings.get("local", {})
+    if not local.get("url") or not local.get("token"):
+        return JSONResponse(
+            status_code=400,
+            content={"detail": "Local instance not configured — set LOCAL_OUTLINE_URL and LOCAL_OUTLINE_TOKEN env vars"},
+        )
+    job_id = _new_job("compare")
+    return {"job_id": job_id, "stream_url": f"/stream/{job_id}"}
+
+
 @app.post("/push")
 async def start_push():
     if _active_job is not None: