Bootstrap agent-ready docs and permissions (D-036)

Root AGENTS.md is now the single source of truth for coding agents;
CLAUDE.md, GEMINI.md and docs/CLAUDE.md are pointers. The product spec
moves from docs/CLAUDE.md to PRODUCT.md, DESIGN.md records the shipped
visual system, and docs/PERMISSIONS.md defines agent permission tiers
rendered to .claude/, .codex/ and .gemini/. Adds docs/specs/ and
docs/plans/, logs issues noticed (not fixed) in WorkBreakdown.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/Architecture.md

@@ -1,7 +1,7 @@
 # Architecture
 
-> Companion to `CLAUDE.md` (product spec & tooling rules) and `Decisions.md` (why things
-> are the way they are). This file describes **how the system is structured**. Update it
+> Companion to `../PRODUCT.md` (product spec), `../AGENTS.md` (agent & tooling rules) and
+> `Decisions.md` (why things are the way they are). This file describes **how the system is structured**. Update it
 > whenever the structure changes.
 
 ## 1. System overview