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>

skills/popups/evals/evals.json

@@ -81,10 +81,10 @@
     {
       "id": 6,
       "prompt": "We need to optimize the lead capture form inside our popup. It currently asks for name, email, company, and phone number. Too many fields?",
-      "expected_output": "Should recognize this overlaps with form optimization. Should defer to or cross-reference the form-cro skill, which handles form field optimization, layout, and conversion. May provide popup-specific context (popups need minimal fields due to fleeting attention) but should make clear that form-cro is the right skill for detailed form optimization.",
+      "expected_output": "Should recognize this overlaps with form optimization. Should defer to or cross-reference the cro skill, which handles form field optimization, layout, and conversion. May provide popup-specific context (popups need minimal fields due to fleeting attention) but should make clear that cro is the right skill for detailed form optimization.",
       "assertions": [
         "Recognizes overlap with form optimization",
-        "References or defers to form-cro skill",
+        "References or defers to cro skill",
         "Notes popups need minimal fields due to context",
         "Does not attempt detailed form redesign"
       ],