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/lib/api.ts

@@ -46,7 +46,16 @@ export interface Stats {
 async function getJson<T>(path: string): Promise<T> {
   const res = await fetch(path)
   if (!res.ok) {
-    throw new Error(`${path} failed: ${res.status}`)
+    let message = `${path} failed: ${res.status}`
+    try {
+      const body: unknown = await res.json()
+      if (body && typeof body === 'object' && 'error' in body && typeof (body as { error: unknown }).error === 'string') {
+        message = (body as { error: string }).error
+      }
+    } catch {
+      // body wasn't JSON (or had no `error` field) — fall back to the generic message
+    }
+    throw new Error(message)
   }
   return res.json() as Promise<T>
 }
@@ -56,12 +65,14 @@ export function fetchLogs(params: {
   startMs?: number
   endMs?: number
   limit?: number
+  filter?: string
 }): Promise<LogEntry[]> {
   const search = new URLSearchParams()
   if (params.sinceSequence !== undefined) search.set('since_sequence', String(params.sinceSequence))
   if (params.startMs !== undefined) search.set('start_ms', String(params.startMs))
   if (params.endMs !== undefined) search.set('end_ms', String(params.endMs))
   if (params.limit !== undefined) search.set('limit', String(params.limit))
+  if (params.filter) search.set('filter', params.filter)
   return getJson(`/api/logs?${search.toString()}`)
 }
 
@@ -69,11 +80,13 @@ export function fetchTimeline(params: {
   startMs?: number
   endMs?: number
   bucketMs?: number
+  filter?: string
 }): Promise<TimelineBucket[]> {
   const search = new URLSearchParams()
   if (params.startMs !== undefined) search.set('start_ms', String(params.startMs))
   if (params.endMs !== undefined) search.set('end_ms', String(params.endMs))
   if (params.bucketMs !== undefined) search.set('bucket_ms', String(params.bucketMs))
+  if (params.filter) search.set('filter', params.filter)
   return getJson(`/api/timeline?${search.toString()}`)
 }