Make Scan Plugins a viable required check; auto-dispatch on bump PRs (#1815)

Scan Plugins is meant to gate every change to marketplace.json, but two
gaps made that unenforceable:

1. The bump workflow opens PRs with GITHUB_TOKEN, which GitHub exempts
   from on:pull_request triggers. Weekly bump PRs (e.g. #1809) get no
   scan check at all.
2. The workflow had a paths filter, so a required-check ruleset for
   `scan` would block every PR that doesn't touch marketplace.json
   (no check run = pending forever).

Fixes:

scan-plugins.yml
- Drop the paths filter; replace with a step-level `git diff --quiet`
  early-exit on the same paths. The check now reports on every PR,
  which makes it safe to require.
- Fail closed when ANTHROPIC_API_KEY is unset and a scan is needed.
  The shared action no-ops gracefully in that case (right default for
  community repos), but a required check that silently does nothing is
  a rubber stamp.

bump-plugin-shas.yml
- After the action opens the bump PR, `gh workflow run scan-plugins.yml
  --ref bump/plugin-shas`. workflow_dispatch is exempt from the
  GITHUB_TOKEN recursion guard, and the resulting check run lands on
  the branch HEAD (= PR head), so it satisfies the required check.
- Add `actions: write` so the dispatch is allowed.

Follow-up: add a repo ruleset on main requiring the `scan` check
(integration: github-actions) once this merges.

.claude-plugin/marketplace.json

@@ -81,6 +81,22 @@
       },
       "homepage": "https://github.com/AikidoSec/aikido-claude-plugin"
     },
+    {
+      "name": "airtable",
+      "description": "Airtable is the database and operations layer for your agents — whether running product, marketing, sales, ops, HR, or a custom business app. It combines structured data with multiplayer visual surfaces (grid, kanban, calendar, gallery, timeline) humans and agents share — plus sync integrations to Jira, Salesforce, Zendesk, Google Drive, Databricks, and the rest of your stack, all backed by enterprise governance. This plugin makes Claude fluent in Airtable: creating bases and schema, working with records, and sharing UI for collaboration. Bundles the official Airtable MCP server.",
+      "author": {
+        "name": "Airtable"
+      },
+      "category": "productivity",
+      "source": {
+        "source": "git-subdir",
+        "url": "https://github.com/Airtable/skills.git",
+        "path": "plugins/airtable",
+        "ref": "main",
+        "sha": "aaeb4f3ec8d462d694a13fe5c3d249c291bf8899"
+      },
+      "homepage": "https://www.airtable.com"
+    },
     {
       "name": "alloydb",
       "description": "Create, connect, and interact with an AlloyDB for PostgreSQL database and data.",