Wire @crema/agent-ui: ToolCallCard + AgentAvatar with activity

The /ai surface now renders agent-ui primitives instead of homegrown
tool/typing widgets:

- AgentAvatar with activity (thinking / working / waiting / speaking /
  idle) replaces TypingIndicator. Pulses while the model is generating,
  shows "waiting" while a write is held for confirmation, "working" while
  a confirmed write is executing, "speaking" once tokens are streaming.
- ToolCallCard renders each native tool_call with typed status (pending
  / running / success / error). Built from the assistant message's
  toolCalls plus the matching tool result message. Tool messages no
  longer render standalone — absorbed into their parent assistant turn.
- Empty assistant bubbles (no prose, only tool_calls) collapse so the
  ToolCallCards carry the visual weight.

Wiring: add @crema/agent-ui path entry to tsconfig and @source line to
app.css. Sibling lib-agent-ui must be cloned next to arcadia-admin.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/app.css

@@ -17,6 +17,7 @@
 @source "../../lib-search-ui/src";
 @source "../../lib-feedback-ui/src";
 @source "../../lib-auth-ui/src";
+@source "../../lib-agent-ui/src";
 /* CREMA:SOURCES */
 
 @custom-variant dark (&:is(.dark *));