test(validation): add Pester tests for Validate-SkillFormat.ps1

100% code coverage with 32 tests covering:
- Path parameter validation (empty, non-existent)
- Index file exclusion (skills-*-index.md, memory-index.md)
- Atomic format detection (PASS for single skill)
- Bundled format detection (FAIL for multiple skills)
- CI mode exit codes (1 for bundled files)
- StagedOnly mode with git integration
- Output message validation

Also updates copilot-pr-review memory with PR #308 statistics:
signal improved from 21% to 62%.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: rjmurillo-bot

.serena/memories/copilot-pr-review.md

@@ -15,11 +15,16 @@
 | PowerShell escapes (`` `a ``, `` `n ``) | Skip |
 | Duplicates cursor[bot] | Note duplicate |
 
-## Metrics (PR #249)
+## Metrics
 
-Signal: 21% (↓ from 35%) | False positives: 64% (↑ from 10%)
+| PR | Signal | False Positives | Notes |
+|----|--------|-----------------|-------|
+| #249 | 21% | 64% | High noise, cursor[bot] duplicates |
+| #308 | 62% | 38% | Table-only format FPs (4), phrasing FPs (2) |
 
-**→ Prioritize cursor[bot] first. Increase verification.**
+**Trend**: Signal improved 41 points. New ADR-017 table-only format not yet learned by Copilot.
+
+**→ Document table-only format in coderabbit config to reduce FPs.**
 
 ## Response Templates