fix(test): randomize tag name in push-enabled fixture

the branch name was already randomized with \${RANDOM}, but the tag
name was hardcoded as `test-tag-enabled`. every successful run left
that tag on the fixture remote with no cleanup, so subsequent runs'
checkouts (which fetch tags) saw the local tag already exist and
failed with `fatal: tag already exists`. the agent's git-push fallback
then hit the deliberately-broken creds and the test scored
push_tags=✗ delete_branch=✗.

mirror the branch pattern with \${RANDOM} so every run gets a fresh
tag name. tags still accumulate on the remote but no longer collide;
that's an infra cleanup concern, not a correctness one.

test/agnostic/pushEnabled.ts

@@ -18,8 +18,8 @@ const fixture = defineFixture(
 3. Report if it succeeded
 
 ## Test 2: Tag Operations
-1. Create a local tag using the git MCP tool: git tag -a test-tag-enabled -m "test tag"
-2. Try push_tags tool with tag "test-tag-enabled"
+1. Create a local tag using the git MCP tool: git tag -a test-tag-enabled-\${RANDOM} -m "test tag"
+2. Try push_tags tool with the tag you just created
 3. Report if tag push succeeded
 
 ## Test 3: Branch Deletion (cleanup)