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/0006-install-always-overwrites.md

@@ -0,0 +1,3 @@
+# install.sh always overwrites deployed files
+
+`install.sh` overwrites `~/.claude/` and `~/.claude/core/` unconditionally on every run. It does not merge, diff, or ask. The rationale: the source of truth is this repo. Editing deployed files directly is a usage error — `sync.sh` would overwrite those edits on the next pull anyway. Offering a merge path would imply that editing `~/.claude/CLAUDE.md` directly is a supported workflow, which it is not. If a local customisation is needed it belongs in a project-level override file, not in the deployed global config.