[codex] Sync Figma skills to v2.2.0

[ashwinm-oai]

Summary

• Sync upstream Figma skills from figma/mcp-server-guide@15599e7 (v2.2.0).
• Preserve the existing repository mapping of upstream skills/figma-code-connect into plugins/figma/skills/figma-code-connect-components while exposing the skill name figma-code-connect.
• Add upstream figma-generate-diagram, figma-use-figjam, and figma-use-slides with the repository Figma license and OpenAI agent metadata conventions.
• Keep repo-only figma-implement-design and figma-create-design-system-rules pinned to the older upstream ref because Figma removed those skills upstream.
• Update Figma plugin metadata, lock entries, and Code Connect command/agent wording so the local surface lines up with the synced skills.

Validation

• jq empty plugins/figma/.codex-plugin/plugin.json plugins/figma/plugin.lock.json plugins/figma/.app.json plugins/figma/hooks.json
• Skill-name scan: 10 Figma skills, no duplicate exposed names.
• git diff --cached --check