chore: bootstrap repo with chunks 1 and 2

Establishes the global AI development config repo from scratch:

- Chunk 1: repo skeleton, install.sh, statusline, deploy manifest
- Chunk 2: core instructions (coding/git/testing), CLAUDE.md rewrite
  (always-on + content index two-tier model), docs restructure,
  6 ADRs, ROADMAP.md, .gitkeep placeholders
- Bootstrap skills in .claude/skills/ (to be catalogued and migrated
  to .agents/skills/ in Chunk 3)

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

docs/adr/0004-skills-in-agents-dir.md

@@ -0,0 +1,3 @@
+# Skills live in .agents/skills/, not .claude/skills/
+
+Skills (slash commands) are stored in `.agents/skills/` following the [Agent Skills open standard](https://agentskills.io), not in `.claude/skills/` which is a Claude Code-specific location. Claude Code, GitHub Copilot, Cursor, and other tools read `.agents/skills/` natively without an adapter. Putting skills in `.claude/skills/` would make them Claude Code-only and contradict ADR-0003 (provider-agnostic where possible). Skills are the strongest shared primitive across providers — they should live at the most portable location available.