Fix CI failures: restore root bin/shakapacker-config and fix prettier (#858)

## Summary

- Restores `bin/shakapacker-config` at project root (was moved by PR
#841, breaking integration tests)
- Fixes quote style in `spec/dummy/bin/shakapacker-config` to match
local `.prettierrc.yaml` (single quotes)

This fixes two pre-existing CI failures that appear on the main branch:
1. **Node based checks (Linting)** - Prettier failing on
`spec/dummy/bin/shakapacker-config`
2. **Testing (ubuntu-latest, 20.x/22.x)** - Integration tests can't find
`bin/shakapacker-config`

## Test plan

- [x] Verified locally: `yarn prettier --check .` passes
- [x] Verified locally: `yarn lint` passes  
- [x] Verified locally: `yarn test` passes (319 tests)
- [ ] CI should pass with these changes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: justin808

bin/shakapacker-config

@@ -0,0 +1,11 @@
+#!/usr/bin/env node
+
+// Minimal shim - all logic is in the TypeScript module
+const { run } = require("shakapacker/configExporter")
+
+run(process.argv.slice(2))
+  .then((exitCode) => process.exit(exitCode))
+  .catch((error) => {
+    console.error(error.message)
+    process.exit(1)
+  })

spec/dummy/bin/shakapacker-config

@@ -1,7 +1,7 @@
 #!/usr/bin/env node
 
 // Minimal shim - all logic is in the TypeScript module
-const { run } = require("shakapacker/configExporter")
+const { run } = require('shakapacker/configExporter')
 
 run(process.argv.slice(2))
   .then((exitCode) => process.exit(exitCode))