fix(test): fix parallel test server isolation — remove shared ctx.port fallback

## Summary

- Replace `|| ctx.port` shared-context fallback with a hard assertion in all four test modules (`client-typescript`, `client-python`, `client-mcp`, `nodes`); each module already starts its own server on a dynamically assigned port (`--port=0`), but the fallback silently routed subprocesses to whichever module's port was written last to the shared Listr2 context
- Remove the `-s` sequential workaround from CI (added in #734) — parallel execution is now safe by construction
- Update stale `:5565` comment in `_build.yaml` to reflect dynamic per-module port allocation

## Type

fix

## Testing

- [ ] Tests added or updated
- [x] Tested locally
- [ ] `./builder test` passes

## Checklist

- [x] Commit messages follow [conventional commits](https://www.conventionalcommits.org/)
- [x] No secrets or credentials included
- [ ] Wiki updated (if applicable)
- [ ] Breaking changes documented (if applicable)

## Linked Issue

Fixes #741

Author: asclearuc

.github/workflows/_build.yaml

@@ -124,15 +124,16 @@ jobs:
 
       - name: Test
         if: inputs.codeql == false
-        # Integration tests boot a local server on :5565 and connect a test
-        # client. Both sides need the same shared secret to authenticate;
-        # without ROCKETRIDE_APIKEY the server raises AuthenticationException
-        # and the client tests fail with "No authentication configured".
-        # The secret value itself doesn't matter — it just has to match
-        # between server and client in this single CI run.
+        # Each test module boots its own server on a dynamically assigned port
+        # (--port=0) and connects via ROCKETRIDE_URI set per subprocess. Both
+        # sides need the same shared secret to authenticate; without
+        # ROCKETRIDE_APIKEY the server raises AuthenticationException and the
+        # client tests fail with "No authentication configured". The secret
+        # value itself doesn't matter — it just has to match between server
+        # and client in this single CI run.
         env:
           ROCKETRIDE_APIKEY: ${{ secrets.ROCKETRIDE_APIKEY }}
-        run: ${{ matrix.builder_cmd }} test --verbose -s
+        run: ${{ matrix.builder_cmd }} test --verbose
 
       - name: Perform CodeQL Analysis
         if: inputs.codeql && matrix.platform == 'ubuntu'