feat: support and test MDCPS reviewer identity per #107

- Update v2 test config: mdcps reviewer username '913443' (distinct from author 'jcwalker3'), author 'jcwalker3'
- Adjust TBD negative test to use mutate (post-provisioning)
- Add mdcps-reviewer example to gitea-mcp.example.json and README
- Verifies distinct identities, reviewer cannot create/push, author cannot review/merge

Closes #107

Checks:
- config tests pass
- no secrets in changes (usernames only)
- py_compile and diff clean

README.md

@@ -221,6 +221,12 @@ Canonical profile file (e.g. `~/.config/gitea-tools/profiles.json`):
       "username": "913443",
       "auth": { "type": "env", "name": "GITEA_TOKEN_MDCPS" },
       "execution_profile": "mdcps"
+    },
+    "mdcps-reviewer": {
+      "base_url": "https://gitea.dadeschools.net",
+      "username": "913443",
+      "auth": { "type": "keychain", "id": "mdcps.gitea.reviewer.token" },
+      "execution_profile": "mdcps-reviewer"
     }
   }
 }