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>

commands/prune.md

@@ -0,0 +1,31 @@
+---
+name: prune
+description: Delete pending instincts older than 30 days that were never promoted
+command: true
+---
+
+# Prune Pending Instincts
+
+Remove expired pending instincts that were auto-generated but never reviewed or promoted.
+
+## Implementation
+
+Run the instinct CLI using the plugin root path:
+
+```bash
+python3 "${CLAUDE_PLUGIN_ROOT}/skills/continuous-learning-v2/scripts/instinct-cli.py" prune
+```
+
+Or if `CLAUDE_PLUGIN_ROOT` is not set (manual installation):
+
+```bash
+python3 ~/.claude/skills/continuous-learning-v2/scripts/instinct-cli.py prune
+```
+
+## Usage
+
+```
+/prune                    # Delete instincts older than 30 days
+/prune --max-age 60      # Custom age threshold (days)
+/prune --dry-run         # Preview without deleting
+```