feat: persistent per-application config with GET/PUT endpoints

Add application_config table (V4 migration), repository, and REST
controller. GET /api/v1/config/{app} returns config, PUT saves and
pushes CONFIG_UPDATE to all LIVE agents via SSE. UI tracing toggle
now uses config API instead of direct SET_TRACED_PROCESSORS command.
Tracing store syncs with server config on load.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/stores/tracing-store.ts

@@ -8,6 +8,8 @@ interface TracingState {
   isTraced: (app: string, processorId: string) => boolean
   /** Toggle processor tracing (BOTH on, remove on off). Returns the full map for the app. */
   toggleProcessor: (app: string, processorId: string) => Record<string, CaptureMode>
+  /** Sync store with server-side config (called when config is fetched). */
+  syncFromServer: (app: string, tracedProcessors: Record<string, string>) => void
 }
 
 export const useTracingStore = create<TracingState>((set, get) => ({
@@ -25,4 +27,14 @@ export const useTracingStore = create<TracingState>((set, get) => ({
     }))
     return current
   },
+
+  syncFromServer: (app, serverMap) => {
+    const mapped: Record<string, CaptureMode> = {}
+    for (const [k, v] of Object.entries(serverMap)) {
+      mapped[k] = v as CaptureMode
+    }
+    set((state) => ({
+      tracedProcessors: { ...state.tracedProcessors, [app]: mapped },
+    }))
+  },
 }))