feat(plugin): fix guardian hooks, add InstructionsLoaded enforcement, .claude/rules emitter, AGENTS.md interop

Closes the gap between ClaudeForge and the Anthropic docs at
code.claude.com/docs/en/memory (and its linked hooks / skills / plugins
pages). Five tightly-scoped changes, each verified by smoke test.

A. Fix guardian hook frontmatter shape (agent/claude-md-guardian.md)

   The previous array-of-{event, commands} shape did not match the
   documented schema (hooks: { EventName: [{ matcher, hooks: [{ type,
   command }] }] }), so the guardian's hooks silently did not fire.
   Rewritten to the canonical keyed-object shape with PostToolUse,
   PreToolUse, SessionStart, and the new InstructionsLoaded event.

B+C. Plugin-level hooks/hooks.json + hooks/validate-claude-md.py

   New deterministic enforcement of the 150-line cap. The validator
   script reads the hook payload from stdin, extracts any referenced
   CLAUDE.md path (supports both PostToolUse tool_input.file_path and
   InstructionsLoaded path / file shapes), and exits 2 with stderr
   feedback when the file is over 150 lines. Wired to both PostToolUse
   on Write|Edit and InstructionsLoaded on every load_reason
   (session_start, nested_traversal, path_glob_match, include, compact).
   The cap is now enforced at every load *and* write, not only when the
   guardian decides to run sync.

D. ContentGenerator.generate_rules_file() (skill/generator.py)

   Emits path-scoped .claude/rules/*.md instruction files with name,
   description, and paths: glob frontmatter. Claude loads these
   lazily — only when accessing files matching the globs — so
   file-type-specific guidance no longer has to live in the root
   CLAUDE.md. Validates that paths is non-empty (ValueError otherwise).

E. AGENTS.md / .cursorrules / .windsurfrules interop

   command/enhance-claude-md.md Phase 1 now lists which sibling
   instruction files exist. ContentGenerator.generate_root_file() reads
   project_context['existing_instruction_files'] and prepends an
   ## External Instructions section with @AGENTS.md (etc.) imports, so
   repos already using other agent tooling can adopt ClaudeForge
   without losing their existing instructions.

Smoke tests (all pass):
- Guardian hooks frontmatter parses as a dict with 4 events, each
  carrying matcher + nested hooks array of {type, command} entries.
- hooks.json is valid JSON; PostToolUse matcher = Write|Edit;
  InstructionsLoaded matcher covers all five load_reason values.
- validate-claude-md.py: small file -> rc 0, bloated file (200 lines)
  -> rc 2 with stderr referencing the 150 cap, InstructionsLoaded
  payload shape also handled, non-CLAUDE.md paths ignored, no stdin
  -> rc 0.
- generate_rules_file emits valid frontmatter with paths glob and
  raises ValueError when paths is empty.
- generate_root_file inserts @AGENTS.md and @.cursorrules imports
  when existing_instruction_files lists them; omits the section
  otherwise.
- Regression: large-fullstack root still 52 lines with chain imports
  intact; all five sub-CLAUDE.md files in this repo still pass
  validator (status = pass).

Docs:
- agent/CLAUDE.md updated to show the canonical hook shape and the
  hook-driven validator wiring.
- skill/CLAUDE.md notes generate_rules_file and AGENTS.md interop.
- CHANGELOG.md documents all five changes under Unreleased.

skill/CLAUDE.md

@@ -31,7 +31,7 @@ Five modules live under `skill/`:
 - **`analyzer.py`** — `CLAUDEMDAnalyzer`: analyses existing files; quality scoring (0–100) across length, completeness, formatting, specificity, modularity.
 - **`validator.py`** — `BestPracticesValidator`: checks file length (hard cap 150, warning at 120), required sections, formatting, anti-patterns.
 - **`template_selector.py`** — `TemplateSelector`: maps project type + team size to a template; all team-size targets are ≤ 150 lines.
-- **`generator.py`** — `ContentGenerator`: writes root + context files, emits `@path` chain imports, prepends sub-file back-links, idempotent `merge_with_existing`.
+- **`generator.py`** — `ContentGenerator`: writes root + context files, emits `@path` chain imports, prepends sub-file back-links, idempotent `merge_with_existing`. Also exposes `generate_rules_file(name, description, paths, body)` for path-scoped `.claude/rules/*.md` files (loaded lazily by Claude when accessed files match the `paths:` globs) and prepends `@AGENTS.md`-style imports when `project_context['existing_instruction_files']` lists sibling instruction files.
 
 ## Required Output Sections