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/free-tools/evals/evals.json

@@ -77,10 +77,10 @@
     {
       "id": 6,
       "prompt": "How do I optimize the landing page for our free tool to get more signups? The tool itself is great but nobody finds it.",
-      "expected_output": "Should recognize this is a landing page conversion optimization task, not a free tool strategy task. Should defer to or cross-reference the page-cro skill for optimizing the tool's landing page conversion rate. May provide free-tool-specific context (gating strategy, value demonstration) but should make clear that page-cro is the right skill for page conversion optimization.",
+      "expected_output": "Should recognize this is a landing page conversion optimization task, not a free tool strategy task. Should defer to or cross-reference the cro skill for optimizing the tool's landing page conversion rate. May provide free-tool-specific context (gating strategy, value demonstration) but should make clear that cro is the right skill for page conversion optimization.",
       "assertions": [
         "Recognizes this as page CRO, not free tool strategy",
-        "References or defers to page-cro skill",
+        "References or defers to cro skill",
         "May provide free-tool-specific context",
         "Does not attempt full page CRO using free tool strategy patterns"
       ],