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/pages/ExchangeDetail/ExchangeDetail.tsx

@@ -1,4 +1,4 @@
-import { useState, useMemo, useCallback } from 'react'
+import { useState, useMemo, useCallback, useEffect } from 'react'
 import { useParams, useNavigate } from 'react-router'
 import {
   Badge, StatusDot, MonoText, CodeBlock, InfoCallout,
@@ -10,7 +10,7 @@ import { useCorrelationChain } from '../../api/queries/correlation'
 import { useDiagramLayout } from '../../api/queries/diagrams'
 import { mapDiagramToRouteNodes } from '../../utils/diagram-mapping'
 import { useTracingStore } from '../../stores/tracing-store'
-import { useSendGroupCommand } from '../../api/queries/commands'
+import { useApplicationConfig, useUpdateApplicationConfig } from '../../api/queries/commands'
 import styles from './ExchangeDetail.module.css'
 
 // ── Helpers ──────────────────────────────────────────────────────────────────
@@ -187,27 +187,35 @@ export default function ExchangeDetail() {
   // ── Tracing toggle ──────────────────────────────────────────────────────
   const { toast } = useToast()
   const tracingStore = useTracingStore()
-  const sendCommand = useSendGroupCommand()
   const app = detail?.applicationName ?? ''
+  const { data: appConfig } = useApplicationConfig(app || undefined)
+  const updateConfig = useUpdateApplicationConfig()
+
+  // Sync tracing store with server config
+  useEffect(() => {
+    if (appConfig?.tracedProcessors && app) {
+      tracingStore.syncFromServer(app, appConfig.tracedProcessors)
+    }
+  }, [appConfig, app])
 
   const handleToggleTracing = useCallback((processorId: string) => {
-    if (!processorId || !detail?.applicationName) return
+    if (!processorId || !detail?.applicationName || !appConfig) return
     const newMap = tracingStore.toggleProcessor(app, processorId)
-    sendCommand.mutate({
-      group: detail.applicationName,
-      type: 'set-traced-processors',
-      payload: { processors: newMap },
-    }, {
-      onSuccess: (data) => {
+    const updatedConfig = {
+      ...appConfig,
+      tracedProcessors: { ...newMap },
+    }
+    updateConfig.mutate(updatedConfig, {
+      onSuccess: (saved) => {
         const action = processorId in newMap ? 'enabled' : 'disabled'
-        toast({ title: `Tracing ${action}`, description: `${processorId} — sent to ${data?.targetCount ?? 0} agent(s)`, variant: 'success' })
+        toast({ title: `Tracing ${action}`, description: `${processorId} — config v${saved.version}`, variant: 'success' })
       },
       onError: () => {
         tracingStore.toggleProcessor(app, processorId)
-        toast({ title: 'Command failed', description: 'Could not send tracing command', variant: 'error' })
+        toast({ title: 'Config update failed', description: 'Could not save configuration', variant: 'error' })
       },
     })
-  }, [detail, app, tracingStore, sendCommand, toast])
+  }, [detail, app, appConfig, tracingStore, updateConfig, toast])
 
   // Correlation chain
   const correlatedExchanges = useMemo(() => {
@@ -372,7 +380,7 @@ export default function ExchangeDetail() {
                   return [{
                     label: tracingStore.isTraced(app, pid) ? 'Disable Tracing' : 'Enable Tracing',
                     onClick: () => handleToggleTracing(pid),
-                    disabled: sendCommand.isPending,
+                    disabled: updateConfig.isPending,
                   }]
                 }}
               />
@@ -391,7 +399,7 @@ export default function ExchangeDetail() {
                   return [{
                     label: tracingStore.isTraced(app, pid) ? 'Disable Tracing' : 'Enable Tracing',
                     onClick: () => handleToggleTracing(pid),
-                    disabled: sendCommand.isPending,
+                    disabled: updateConfig.isPending,
                   }]
                 }}
               />