Add Airtable Codex plugin

[ashwinm-oai]

Summary:

• Import upstream Airtable skills plugin as a clean first commit.
• Replace Airtable MCP config with app connector id asdk_app_693ca6ce2db08191bb52d66743c65184.
• Restore upstream Airtable metadata where possible while keeping required Codex schema and app-connector changes.

Validation:

• node plugins/plugin-eval/scripts/plugin-eval.js analyze plugins/airtable --format markdown (score 86/100; no failures, expected static budget/description warnings from upstream content).