feat: consolidate page-cro and form-cro into unified cro skill

- Create skills/cro/ with shared CRO analysis framework
- Move page-specific content to references/page.md
- Move form-specific content to references/form.md
- Copy experiments reference from page-cro
- Remove skills/page-cro/ and skills/form-cro/
- Update all cross-references across skills, tools, README, AGENTS.md

BREAKING: page-cro and form-cro are replaced by cro.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

AGENTS.md

@@ -74,7 +74,7 @@ description: What this skill does and when to use it. Include trigger phrases.
 - No consecutive hyphens (`--`)
 - Must match parent directory name exactly
 
-**Valid**: `page-cro`, `emails`, `ab-testing`
+**Valid**: `cro`, `emails`, `ab-testing`
 **Invalid**: `Page-CRO`, `-page`, `page--cro`
 
 ### Optional Skill Directories
@@ -151,7 +151,7 @@ See [Claude Code plugins documentation](https://code.claude.com/docs/en/plugins.
 Follow the [Conventional Commits](https://www.conventionalcommits.org/) specification:
 
 - `feat: add skill-name skill`
-- `fix: improve clarity in page-cro`
+- `fix: improve clarity in cro`
 - `docs: update README`
 
 ### Pull Request Checklist