The frontend fix alone wasn't enough because:
1. serveIndexHtml() was injecting the raw avatar filename into HTML
2. agent.identity.get RPC was returning raw filename, overwriting the
   HTML-injected value

Now both paths resolve local file avatars (*.png, *.jpg, etc.) to the
/avatar/{agentId} endpoint URL.

- Add computeAdaptiveChunkRatio() to reduce chunk size for large messages
- Add isOversizedForSummary() to detect messages too large to summarize
- Add summarizeWithFallback() with progressive fallback:
  - Tries full summarization first
  - Falls back to partial summarization excluding oversized messages
  - Notes oversized messages in the summary output
- Add SAFETY_MARGIN (1.2x) buffer for token estimation inaccuracy
- Reduce MIN_CHUNK_RATIO to 0.15 for very large messages

This prevents compaction failures when conversations contain
unusually large tool outputs or responses that exceed the
summarization model's context window.

Compaction indicator:
- Add CompactionStatus type and handleCompactionEvent() in app-tool-stream.ts
- Show '🧹 Compacting context...' toast while active (with pulse animation)
- Show '🧹 Context compacted' briefly after completion
- Auto-clear toast after 5 seconds
- Add CSS styles for .callout.info, .callout.success, .compaction-indicator

Error handling improvements:
- Wrap onEvent callback in try/catch in gateway.ts to prevent errors
  from breaking the WebSocket message handler
- Wrap handleGatewayEvent in try/catch with console.error logging
  to isolate errors and make them visible in devtools

These changes address UI freezes during heavy agent activity by:
1. Showing users when compaction is happening
2. Preventing uncaught errors from silently breaking the event loop

TypeScript inferred the union type without agentId when falling back to
DEFAULT_ASSISTANT_IDENTITY, causing build errors at control-ui.ts:222-223.