feat(extension-api): npm package + TypeDoc→MDX docgen + CI workflows (PKG3/4/5)

- packages/extension-api/: @comfyorg/extension-api npm package wrapper
  (src/, package.json, README.md, tsconfig{,.build,.docs}.json,
  typedoc.json, scripts/build-docs.ts, .npmignore, .gitignore)
- .github/workflows/extension-api-typecheck.yml (PKG4.D3)
- .github/workflows/extension-api-publish.yml (PKG4.D4)
- scripts/generate-docs.sh (PKG5.D6)
- pnpm-lock.yaml: workspace dependency for new package

Sidecar: independent of i-foundation; stacks directly on PR #2.

scripts/generate-docs.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# PKG5.D6 — Generate TypeDoc → Mintlify MDX for @comfyorg/extension-api
+#
+# Output: packages/extension-api/docs-build/mintlify/*.mdx
+#         packages/extension-api/docs-build/mintlify/nav-snippet.json
+#
+# Prerequisites: pnpm install must have been run (typedoc, tsx)
+# Usage: ./scripts/generate-docs.sh [--watch]
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+PKG_DIR="$REPO_ROOT/packages/extension-api"
+
+if [ ! -f "$PKG_DIR/package.json" ]; then
+  echo "ERROR: $PKG_DIR/package.json not found — run from repo root or ensure packages/extension-api exists." >&2
+  exit 1
+fi
+
+if [ "${1:-}" = "--watch" ]; then
+  echo "Starting docs watch mode..."
+  pnpm --filter @comfyorg/extension-api docs:watch
+else
+  echo "Generating extension API docs..."
+  pnpm --filter @comfyorg/extension-api docs:build
+  echo ""
+  echo "Done. MDX files written to: $PKG_DIR/docs-build/mintlify/"
+  echo "Copy to Comfy-Org/docs: cp -r $PKG_DIR/docs-build/mintlify/* <docs-repo>/extensions/api/"
+fi