Make the comment's opt-out findable: link to the docs Action section, name the upload

A user who got the comment via a moving action ref (not a deliberate opt-in)
is the one most likely to want to turn it off. Two changes so they find how:
- link 'oasdiff GitHub Action' to /docs/free-review#github-action, the section
  that explains what posted the comment and how to disable it;
- reframe the off-switch from 'stop posting this comment' to 'turn this off
  (no spec upload, no comment)', since review: false stops the upload too,
  which is what a privacy-minded first-time reader actually wants.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: reuvenharrison

breaking/entrypoint.sh

@@ -70,7 +70,7 @@ The link expires in 7 days.
 
 🔒 Your API specs are encrypted in CI before they're uploaded. The decryption key stays in this link's URL fragment (after the #), which browsers never send to a server, so oasdiff cannot read your specs. [How it works →](https://www.oasdiff.com/docs/free-review#privacy)
 
-<sub>Posted automatically by the oasdiff GitHub Action. To stop posting this comment, set \`review: false\` on the action.</sub>"
+<sub>Posted automatically by the [oasdiff GitHub Action](https://www.oasdiff.com/docs/free-review#github-action). To turn this off (no spec upload, no comment), set \`review: false\` on the action.</sub>"
     elif [ -n "$existing_id" ]; then
         body="${marker}
 ### ✅ No breaking changes in the latest revision."

changelog/entrypoint.sh

@@ -89,7 +89,7 @@ The link expires in 7 days.
 
 🔒 Your API specs are encrypted in CI before they're uploaded. The decryption key stays in this link's URL fragment (after the #), which browsers never send to a server, so oasdiff cannot read your specs. [How it works →](https://www.oasdiff.com/docs/free-review#privacy)
 
-<sub>Posted automatically by the oasdiff GitHub Action. To stop posting this comment, set \`review: false\` on the action.</sub>"
+<sub>Posted automatically by the [oasdiff GitHub Action](https://www.oasdiff.com/docs/free-review#github-action). To turn this off (no spec upload, no comment), set \`review: false\` on the action.</sub>"
     elif [ -n "$existing_id" ]; then
         body="${marker}
 ### ✅ No API changes in the latest revision."