Require AI disclosure in expert-reviewer review body

The review body must begin with a 🤖 AI disclosure note so readers
know the review is AI-generated, not human-written. Added as a
non-negotiable delivery rule in Wave 5.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: T-Gro

.github/agents/expert-reviewer.md

@@ -488,7 +488,7 @@ Execute review in five waves, each building on the previous.
    gh api repos/{owner}/{repo}/pulls/{number}/reviews \
      --method POST \
      --field event=COMMENT \
-     --field 'body=Expert AI review — see inline comments for findings.' \
+     --field 'body=*🤖 This review was generated by AI (@expert-reviewer agent). Findings may contain inaccuracies — please verify independently.*' \
      --field 'comments=[
        {"path":"src/Compiler/Checking/CheckDeclarations.fs","line":2750,"body":"**[Test Coverage]** This code path lacks a test. Add a test exercising this branch."},
        {"path":"src/Compiler/CodeGen/IlxGen.fs","line":1234,"body":"**[IL Emission]** Call `stripTyEqns` before this match to handle type abbreviations."}
@@ -502,7 +502,7 @@ Execute review in five waves, each building on the previous.
 3. **If no significant issues found**, post an approving review:
    ```bash
    gh pr review {number} --repo {owner}/{repo} --approve \
-     --body "Expert AI review: no significant issues found across applicable dimensions."
+     --body "*🤖 AI review (@expert-reviewer): no significant issues found across applicable dimensions. Please verify independently.*"
    ```
 
 4. **Apply the label and request human review:**
@@ -511,6 +511,7 @@ Execute review in five waves, each building on the previous.
    ```
 
 **Delivery rules:**
+- The review body MUST begin with an AI disclosure note (the `🤖` line above). This is non-negotiable — readers must know this is AI-generated, not human-written.
 - At most 10 inline comments — prioritize Behavioral over Quality over Nitpick.
 - Every comment must reference a specific file and line from the diff.
 - Never post duplicate content if reviews already exist on the PR.