docs(claude-md): dogfood /sync-claude-md on root CLAUDE.md

Splits the 518-line root CLAUDE.md into a 70-line root plus four chained
sub-files (skill/, command/, agent/, docs/), all under the 150-line cap,
and prunes stale references uncovered by the audit.

- CLAUDE.md (518 -> 70): project overview, navigation with @-imports,
  behavioural guidelines summary, naming reference, license link
- skill/CLAUDE.md (85): component flow, Python module architecture,
  modifying modules, adding templates, tech-stack detection, quality
  scoring, karpathy skill
- command/CLAUDE.md (38): slash command development, top-level .md install
  layout, skill <-> command integration
- agent/CLAUDE.md (70): guardian frontmatter, hook responsibilities,
  skill <-> agent integration, git triggers
- docs/CLAUDE.md (109): install verification, smoke test, manual e2e
  tests, common operations, release process

Stale content removed:
- 'Dual Directory Structure' section (claude-md-enhancer/ legacy dir
  does not exist on disk)
- '20-300 lines' / '300-line cap' references rewritten to 150
- '~/.claude/commands/enhance-claude-md/' bundle paths rewritten to
  top-level '.md' files (matching the new installer layout)
- 'Three integrated components' updated to five
- 'Current Version: 2.0.0' updated to 2.1.0
- '6 examples' in sample_input.json claim corrected (file has 1 scenario)

Each sub-file opens with a markdown back-link and @../CLAUDE.md import;
root contains @-imports for all four sub-files. Validator passes (status
pass) for every file.

agent/CLAUDE.md

@@ -0,0 +1,70 @@
+> Parent context: see the root [CLAUDE.md](../CLAUDE.md) for project-wide guidelines and behavioural rules.
+> Chained import: `@../CLAUDE.md`
+
+# Guardian Agent Development
+
+Guidelines for the `claude-md-guardian` background-maintenance agent.
+
+## File
+
+`agent/claude-md-guardian.md` — installs to `~/.claude/agents/claude-md-guardian.md`.
+
+## Modifying the Agent
+
+1. Edit `agent/claude-md-guardian.md`.
+2. YAML frontmatter fields to preserve:
+   - `permissions: [Bash, Read, Write, Edit, Grep, Glob, Skill]`
+   - `model: haiku` — token efficiency for routine sync runs.
+   - `color: purple` — visual indicator in Claude Code UI.
+   - `fork_safe: true` — agent runs independently.
+   - `hooks: [SessionStart, PreToolUse, PostToolUse]`.
+3. Workflow phases inside the agent:
+   - **Assessment** — read `git diff` / `git status` / changed-file counts.
+   - **Analysis** — decide if changes are significant enough to update CLAUDE.md.
+   - **Update** — invoke the skill for targeted section updates rather than full regeneration (~70–80% token saving vs. rewrite).
+4. Re-install for testing: `cp agent/claude-md-guardian.md ~/.claude/agents/`.
+
+## v2.0.0+ Frontmatter Reference
+
+```yaml
+---
+name: claude-md-guardian
+permissions: [Bash, Read, Write, Edit, Grep, Glob, Skill]
+model: haiku
+color: purple
+fork_safe: true
+hooks:
+  - SessionStart
+  - PreToolUse
+  - PostToolUse
+---
+```
+
+## Skill ↔ Agent Integration
+
+The agent uses `claude-md-enhancer` (the skill's frontmatter name; installed as `claudeforge-skill/`) as its core capability. Invoke it with `Skill: claude-md-enhancer` inside the agent workflow.
+
+Hook responsibilities:
+
+- **SessionStart** — check `git diff`; if significant change is detected, invoke the skill for an incremental update.
+- **PreToolUse** — validate before a CLAUDE.md edit lands.
+- **PostToolUse** — after Edit/Write to any CLAUDE.md, run `BestPracticesValidator`, report the quality score, suggest improvements. Refuse to leave the file over 150 lines.
+
+## Agent ↔ Git
+
+The agent watches for change signals via:
+
+```bash
+git diff --name-status HEAD~10
+git log --since="1 week ago" --oneline --no-merges
+git diff HEAD~10 -- package.json requirements.txt pyproject.toml go.mod Cargo.toml
+```
+
+Triggers an update when any of these hold:
+
+- 5+ files modified since the last sync.
+- New dependencies added to a manifest file.
+- New top-level directories created (potential new sub-CLAUDE.md candidates).
+- Manual invocation after a milestone or release.
+
+When the agent runs sync, it follows `command/sync-claude-md.md`: never commit, leave the diff for the user to review.