Wire FilterBar to server-side filter query language (ticket 016)

Send the raw filter string to GET /api/logs and GET /api/timeline
instead of doing a naive client-side substring match, surface the
API's 400 parse error inline under the FilterBar input, and drop the
now-dead visibleLogs client-side filtering in App.tsx.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/src/App.tsx

@@ -14,6 +14,7 @@ export default function App() {
   const [buckets, setBuckets] = useState<TimelineBucket[]>([])
   const [range, setRange] = useState<TimeRange | null>(null)
   const [filter, setFilter] = useState('')
+  const [filterError, setFilterError] = useState<string | null>(null)
 
   useEffect(() => {
     let cancelled = false
@@ -22,16 +23,19 @@ export default function App() {
       try {
         const [nextStats, nextBuckets, nextLogs] = await Promise.all([
           fetchStats(),
-          fetchTimeline({ startMs: range?.startMs, endMs: range?.endMs }),
-          fetchLogs({ startMs: range?.startMs, endMs: range?.endMs, limit: 1000 }),
+          fetchTimeline({ startMs: range?.startMs, endMs: range?.endMs, filter: filter || undefined }),
+          fetchLogs({ startMs: range?.startMs, endMs: range?.endMs, limit: 1000, filter: filter || undefined }),
         ])
         if (!cancelled) {
           setStats(nextStats)
           setBuckets(nextBuckets)
           setLogs(nextLogs)
+          setFilterError(null)
+        }
+      } catch (err) {
+        if (!cancelled) {
+          setFilterError(err instanceof Error ? err.message : String(err))
         }
-      } catch {
-        // engine not reachable yet; retry on next tick
       }
     }
 
@@ -41,17 +45,15 @@ export default function App() {
       cancelled = true
       clearInterval(id)
     }
-  }, [range])
-
-  const visibleLogs = filter ? logs.filter((l) => l.text.includes(filter)) : logs
+  }, [range, filter])
 
   return (
     <div className="flex h-screen w-screen overflow-hidden">
       <NavMenu stats={stats} />
       <div className="flex min-w-0 flex-1 flex-col">
-        <FilterBar value={filter} onChange={setFilter} />
+        <FilterBar value={filter} onChange={setFilter} error={filterError} />
         <LogTimeline buckets={buckets} range={range} onSelectRange={setRange} />
-        <LogPreview logs={visibleLogs} />
+        <LogPreview logs={logs} />
         <ComingSoon title="Metrics" />
         <ComingSoon title="Dashboards" />
       </div>