docs: consolidate design docs into architecture.md and beads

Replaced 4 individual design docs with single master architecture doc.
Design content moved to bead descriptions (self-contained, no markdown refs).
Closed gt-cr0.

- Add docs/architecture.md: top-down Gas Town explanation
- Delete docs/{town,swarm-shutdown,polecat-beads-access,mayor-handoff}-design.md
- Update CLAUDE.md to point to architecture.md
- Update beads: gt-sd6, gt-f8v, gt-eu9, gt-gl2, gt-zx3, gt-e1y, gt-cjb, gt-082,
  gt-g2d, gt-sye, gt-vci, gt-82y, gt-l3c, gt-u82 now self-contained

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -8,7 +8,7 @@ This is the **Go port** of Gas Town, a multi-agent workspace manager.
 
 - **Issue prefix**: `gt-`
 - **Python version**: ~/ai/gastown-py (reference implementation)
-- **Design docs**: docs/town-design.md
+- **Architecture**: docs/architecture.md
 
 ## Development