ALL-812 — Phase 1 PR 0 — Edges IA restructure + new stubs

Worktree: /home/agent/agents/mono-edges-ia. Branch: anvil/all-812-edges-ia-restructure. Adds Principles/Playbooks/Materials/Accessibility/Agents/Create stubs, updates Nav to 10 sections, retires /content and /guidelines with 301s, expands /components stub to describe 9 job-based groups + short-slug URL rule. NO visual redesign, NO dark-first, NO typography/color changes.