ci: fix Node 20, lint permission, and formatting annotations

[woensug-choi]

CI reports Node 20 deprecations, check-run creation failures (403), and a missing YAML document marker. The lint wrapper also returns success by default when formatting fails, while its formatter versions differ from pre-commit.

This PR fixes those issues together:

• Upgrade JavaScript actions in Docker builds, PR image publishing, and lint to verified Node 24 releases. Keep ShellCheck on a versioned composite action.
• Replace wearerequired/lint-action with direct Black, Flake8, and clang-format checks under a read-only token. This removes the Checks API writes that fail on fork PRs and restricted tokens. Failures now fail the job, while the other lint steps still run.
• Match Black, Flake8, and clang-format versions/settings to pre-commit, eliminating the existing formatter disagreement without reformatting source files.
• Add the missing --- to the MAVROS YAML configuration.
• Add a Pages workflow on Ubuntu 26.04 with Node 24-compatible actions. It preserves the existing Jekyll build from the ros2 repository root and only deploys from ros2; PRs only build and upload a preview artifact. This replaces the GitHub-generated Pages workflow that also emits Node 20 and ubuntu-latest migration annotations.

Validation

• Live Code Formatting Lint and Pages PR build passed. Their check runs have no annotations. Docker builds are still running.

• Actionlint (including ShellCheck) and workflow YAML lint passed.

• Black: all 19 Python files unchanged; Flake8 and clang-format checks passed.

• Repository YAML, shell, and CMake checks passed (13 CMake files).

• Action manifests were checked for runs.using: node24, including the artifact action nested inside the Pages uploader.

• XML lint retains its existing Gazebo namespace diagnostics; no XML source or namespace semantics are changed.

Pages activation after merging

In Settings → Pages → Build and deployment → Source, select GitHub Actions, then run Build and deploy Pages on ros2. The existing Pages source is ros2 /; repository settings have not been changed by this PR. This setting is needed to retire the generated legacy workflow and its uneditable warnings.

Self-hosted runners must support Node 24 (Actions Runner 2.327.1 or newer); current logs already show Node 24 execution. Old run annotations are historical and will remain visible; the fixes apply to new runs.