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/plans/README.md

@@ -0,0 +1,11 @@
+# Plans
+
+Implementation plans from the superpowers writing-plans workflow. **Transient:** a plan lives only while
+its work is in progress and is removed with `git rm` before merging. This README stays.
+
+- Naming: `NNN-short-slug.md`, matching its spec number.
+- Links back to its spec. Bite-sized checkbox tasks with exact file paths, test commands, and
+  commit checkpoints.
+- Written for an engineer with zero context for this codebase — spell out the obvious.
+- Tick checkboxes as you go so another agent can resume an interrupted session.
+- Front matter: `status: draft | approved | in-progress`. There is no `done` — a finished plan is deleted.