Mirrors the amber border styling of council nodes with cyan for debate
nodes, including the icon color and model count subtitle.

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

3-stage council orchestration: parallel model queries (Stage 1),
anonymous peer ranking (Stage 2), and streamed chairman synthesis
(Stage 3). Includes scope-aware file resolution for Google/Claude
providers so upstream file attachments are visible to all providers.

- Backend: council.py orchestrator, /api/run_council_stream endpoint,
  query_model_full() non-streaming wrapper, resolve_provider() helper,
  resolve_scoped_file_ids() for Google/Claude scope parity with OpenAI
- Frontend: council toggle UI, model checkbox selector, chairman picker,
  SSE event parsing, tabbed Stage 1/2/3 response display
- Canvas: amber council node indicator with Users icon

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

Unfold takes a merged trace's messages, extracts the node order,
and creates real edges chaining those nodes sequentially (A→B→C→D→E).
The merged trace is deleted and replaced by a regular pass-through trace.

- Add unfoldMergedTrace() to flowStore (creates edges, rewires downstream)
- Add Unfold button (Layers icon) to Sidebar merged traces UI
- Fix isMerged edge detection to use explicit flag instead of ID prefix
- Fix LLMNode useUpdateNodeInternals deps for dynamic handle updates

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