feat: deep-link Inspect Pipeline button — auto-expand and scroll to video

TechniquePage's 'Inspect pipeline' button passes ?video=<id> to AdminPipeline.
Previously the query param was ignored. Now AdminPipeline reads it on mount,
auto-expands the matching video row, and smooth-scrolls it into view.

frontend/src/pages/AdminPipeline.tsx

@@ -3,7 +3,8 @@
  * expandable event log with token usage and collapsible JSON viewer.
  */
 
-import { useCallback, useEffect, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
+import { useSearchParams } from "react-router-dom";
 import {
   fetchPipelineVideos,
   fetchPipelineEvents,
@@ -448,6 +449,7 @@ function StatusFilter({
 // ── Main Page ────────────────────────────────────────────────────────────────
 
 export default function AdminPipeline() {
+  const [searchParams] = useSearchParams();
   const [videos, setVideos] = useState<PipelineVideoItem[]>([]);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
@@ -456,6 +458,8 @@ export default function AdminPipeline() {
   const [actionMessage, setActionMessage] = useState<{ id: string; text: string; ok: boolean } | null>(null);
   const [activeFilter, setActiveFilter] = useState<string | null>(null);
   const [debugMode, setDebugModeState] = useState<boolean | null>(null);
+  const videoRefs = useRef<Map<string, HTMLDivElement>>(new Map());
+  const deepLinked = useRef(false);
 
   const load = useCallback(async () => {
     setLoading(true);
@@ -474,6 +478,22 @@ export default function AdminPipeline() {
     void load();
   }, [load]);
 
+  // Deep-link: auto-expand and scroll to ?video=<id> on first load
+  useEffect(() => {
+    if (deepLinked.current || loading || videos.length === 0) return;
+    const targetVideoId = searchParams.get("video");
+    if (!targetVideoId) return;
+    const match = videos.find((v) => v.id === targetVideoId);
+    if (!match) return;
+    deepLinked.current = true;
+    setExpandedId(targetVideoId);
+    // Scroll after the expanded detail renders
+    requestAnimationFrame(() => {
+      const el = videoRefs.current.get(targetVideoId);
+      if (el) el.scrollIntoView({ behavior: "smooth", block: "start" });
+    });
+  }, [loading, videos, searchParams]);
+
   useEffect(() => {
     let cancelled = false;
     fetchDebugMode()
@@ -568,7 +588,7 @@ export default function AdminPipeline() {
             {videos
               .filter((v) => activeFilter === null || v.processing_status === activeFilter)
               .map((video) => (
-            <div key={video.id} className="pipeline-video">
+            <div key={video.id} className="pipeline-video" ref={(el) => { if (el) videoRefs.current.set(video.id, el); }}>
               <div
                 className="pipeline-video__header"
                 onClick={() => toggleExpand(video.id)}