feat(odin): OdinChat orchestrator; render on /odin; remove DashAssistant

Wire OdinTabs/OdinThread/InvoiceReviewCard/OdinComposer into a single
OdinChat orchestrator; mount it on /odin (maxWidth 1100); delete the
old DashAssistant and its aiHistoryOptions query helper.

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

src/admin/lib/queries/ai.ts

@@ -59,16 +59,3 @@ export const aiConversationMessagesOptions = (id: number) =>
     staleTime: Infinity,
     gcTime: 0,
   });
-
-export const aiHistoryOptions = () =>
-  queryOptions({
-    queryKey: ["ai", "history"],
-    queryFn: () =>
-      jsonQuery<{ messages: StoredChatMessage[] }>("/api/admin/ai/history"),
-    // Within a mount the thread is seeded once and mutated locally, so don't
-    // refetch on focus (staleTime Infinity). But gcTime 0 drops the cache on
-    // unmount, so every remount re-reads the DB (the source of truth) — this
-    // is what keeps a cleared/appended thread from resurrecting stale messages.
-    staleTime: Infinity,
-    gcTime: 0,
-  });