Fix duplicate message bug and add generation timing instrumentation

Bug fix:
- ChatView.vue onMounted now skips fetchConversation when the conversation
  is already loaded in the store (same guard that the convId watcher uses).
  This prevents duplicate assistant messages when navigating from the
  dashboard inline chat to /chat/:id after streaming completes.

Generation timing:
- logging.py: add log_generation() — persists per-generation timing
  breakdown to app_logs (category=usage, action=generation) including
  model, total_ms, intent_ms, ttft_ms, generation_ms, and per-tool timings.
  Queryable via existing admin log viewer.
- generation_task.py: collect wall-clock timestamps at every pipeline stage:
  intent classification, per-tool execution (both intent-routed and native),
  time-to-first-token (measured from generation start to first content chunk),
  LLM streaming round duration. Logs via log_generation() and includes timing
  in the SSE 'done' event payload.
- types/chat.ts: add GenerationTiming interface; add optional timing field
  to Message.
- chat.ts: capture timing from done event and attach to assistant message.
- ChatMessage.vue: show timing footer on assistant messages with breakdown:
  "⏱ 4.2s total · first token 0.8s · analyzed 0.3s · created event 0.4s
  · generated 3.5s". Visible this session; persisted to app_logs for
  cross-session benchmarking.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/ChatMessage.vue

@@ -3,7 +3,7 @@ import { computed } from "vue";
 import { renderMarkdown } from "@/utils/markdown";
 import { useSettingsStore } from "@/stores/settings";
 import ToolCallCard from "@/components/ToolCallCard.vue";
-import type { Message } from "@/types/chat";
+import type { GenerationTiming, Message } from "@/types/chat";
 
 const settingsStore = useSettingsStore();
 
@@ -34,6 +34,26 @@ const roleLabel = computed(() => {
       return props.message.role;
   }
 });
+
+function formatMs(ms: number | null | undefined): string {
+  if (ms == null) return "";
+  if (ms < 1000) return `${ms}ms`;
+  return `${(ms / 1000).toFixed(1)}s`;
+}
+
+const timingParts = computed((): string[] => {
+  const t = props.message.timing;
+  if (!t) return [];
+  const parts: string[] = [];
+  if (t.total_ms != null) parts.push(`${formatMs(t.total_ms)} total`);
+  if (t.ttft_ms != null) parts.push(`first token ${formatMs(t.ttft_ms)}`);
+  if (t.intent_ms != null) parts.push(`analyzed ${formatMs(t.intent_ms)}`);
+  for (const tool of t.tools ?? []) {
+    parts.push(`${tool.name.replace(/_/g, " ")} ${formatMs(tool.ms)}`);
+  }
+  if (t.generation_ms != null) parts.push(`generated ${formatMs(t.generation_ms)}`);
+  return parts;
+});
 </script>
 
 <template>
@@ -66,6 +86,12 @@ const roleLabel = computed(() => {
         </div>
       </div>
       <span v-if="formattedTime" class="message-timestamp">{{ formattedTime }}</span>
+      <div v-if="timingParts.length" class="message-timing">
+        <span class="timing-icon">⏱</span>
+        <span v-for="(part, i) in timingParts" :key="i" class="timing-part">
+          <span v-if="i > 0" class="timing-sep">·</span>{{ part }}
+        </span>
+      </div>
     </div>
   </div>
 </template>
@@ -193,4 +219,24 @@ const roleLabel = computed(() => {
   margin-top: 0.15rem;
   padding: 0 0.5rem;
 }
+.message-timing {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 0.2rem;
+  padding: 0.1rem 0.5rem 0;
+  font-size: 0.68rem;
+  color: var(--color-text-muted);
+  opacity: 0.7;
+}
+.timing-icon {
+  font-size: 0.65rem;
+}
+.timing-part {
+  white-space: nowrap;
+}
+.timing-sep {
+  margin-right: 0.2rem;
+  opacity: 0.5;
+}
 </style>