#8756 fix(mothership): use a spinner while workflow resources load

Summary

• Replace the text skeleton with a centered loader while workflow resources load in chat.
• Use the loader for code loading, workflow detail resolution, and the metadata cache handoff, with accessible status text and reduced-motion support.

Type of Change

• Bug fix

Testing

• Reviewed all three workflow loading paths and the unchanged query, navigation, and error behavior.
• Ran the cleanup passes, bun run test, bun run lint, bun run type-check, all 58 audits, the block registry check, and bun run docs-manifest:check.
• The app suite passed 35,275 tests. No new tests were added for this presentation-only change.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)