feat(generators): add core-package entry + dispatch table (empty)

Registers pnpm turbo gen core-package with an empty choices list and a
dispatch table that throws for unknown names. Adds vitest config + test
script to turbo/generators and adds it to the pnpm workspace so tests
run via pnpm --filter @repo/turbo-generators test.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pnpm-lock.yaml

@@ -576,6 +576,9 @@ importers:
 
   packages/core-realtime:
     dependencies:
+      '@repo/core-shared':
+        specifier: workspace:*
+        version: link:../core-shared
       payload:
         specifier: ^3.0.0
         version: 3.81.0(graphql@16.13.2)(typescript@5.9.3)
@@ -957,6 +960,12 @@ importers:
         specifier: ^3.1.0
         version: 3.2.4(@types/debug@4.1.13)(@types/node@22.19.17)(happy-dom@20.8.9)(jiti@2.6.1)(jsdom@25.0.1)(lightningcss@1.32.0)(sass@1.99.0)(terser@5.46.2)(tsx@4.21.0)
 
+  turbo/generators:
+    devDependencies:
+      vitest:
+        specifier: ^3.1.0
+        version: 3.2.4(@types/debug@4.1.13)(@types/node@25.5.2)(happy-dom@20.8.9)(jiti@2.6.1)(jsdom@25.0.1)(lightningcss@1.32.0)(sass@1.99.0)(terser@5.46.2)(tsx@4.21.0)
+
 packages:
 
   '@adobe/css-tools@4.4.4':