feat: pending instinct TTL pruning and /prune command (#725)

* feat: add pending instinct TTL pruning and /prune command

Pending instincts generated by the observer accumulate indefinitely
with no cleanup mechanism. This adds lifecycle management:

- `instinct-cli.py prune` — delete pending instincts older than 30 days
  (configurable via --max-age). Supports --dry-run and --quiet flags.
- Enhanced `status` command — shows pending count, warns at 5+,
  highlights instincts expiring within 7 days.
- `observer-loop.sh` — runs prune before each analysis cycle.
- `/prune` slash command — user-facing command for manual pruning.

Design rationale: council consensus (4/4) rejected auto-promote in
favor of TTL-based garbage collection. Frequency of observation does
not establish correctness. Unreviewed pending instincts auto-delete
after 30 days; if the pattern is real, the observer will regenerate it.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

* fix: remove duplicate functions, broaden extension filter, fix prune output

- Remove duplicate _collect_pending_dirs and _parse_created_date defs
- Use ALLOWED_INSTINCT_EXTENSIONS (.md/.yaml/.yml) instead of .md-only
- Track actually-deleted items separately from expired for accurate output
- Update README.md and AGENTS.md command counts: 59 → 60

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

* fix: address Copilot and CodeRabbit review findings

- Use is_dir() instead of exists() for pending path checks
- Change > to >= for --max-age boundary (--max-age 0 now prunes all)
- Use CLV2_PYTHON_CMD env var in observer-loop.sh prune call
- Remove unused source_dupes variable
- Remove extraneous f-string prefix on static string

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

* fix: update AGENTS.md project structure command count 59 → 60

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

* fix: address cubic and coderabbit review findings

- Fix status early return skipping pending instinct warnings (cubic #1)
- Exclude already-expired items from expiring-soon filter (cubic #2)
- Warn on unparseable pending instinct age instead of silent skip (cubic #4)
- Log prune failures to observer.log instead of silencing (cubic #5)

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

* fix: YAML single-quote unescaping, f-string cleanup, add /prune to README

- Fix single-quoted YAML unescaping: use '' doubling (YAML spec) not
  backslash escaping which only applies to double-quoted strings (greptile P1)
- Remove extraneous f-string prefix on static string (coderabbit)
- Add /prune to README command catalog and file tree (cubic)

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

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Happy <yesreply@happy.engineering>

AGENTS.md

@@ -1,6 +1,6 @@
 # Everything Claude Code (ECC) — Agent Instructions
 
-This is a **production-ready AI coding plugin** providing 28 specialized agents, 116 skills, 59 commands, and automated hook workflows for software development.
+This is a **production-ready AI coding plugin** providing 28 specialized agents, 116 skills, 60 commands, and automated hook workflows for software development.
 
 **Version:** 1.9.0
 
@@ -143,7 +143,7 @@ Troubleshoot failures: check test isolation → verify mocks → fix implementat
 ```
 agents/          — 28 specialized subagents
 skills/          — 115 workflow skills and domain knowledge
-commands/        — 59 slash commands
+commands/        — 60 slash commands
 hooks/           — Trigger-based automations
 rules/           — Always-follow guidelines (common + per-language)
 scripts/         — Cross-platform Node.js utilities