refactor: Migrate all lib packages to ESM

Convert all shared library packages from CommonJS to ESM for consistency
with apps/server and modern JavaScript standards.

Changes:
- Add "type": "module" to package.json for all libs
- Update tsconfig.json to use "NodeNext" module/moduleResolution
- Add .js extensions to all relative imports

Packages migrated:
- @automaker/dependency-resolver (already ESM, added .js extension)
- @automaker/git-utils (CommonJS → ESM)
- @automaker/model-resolver (CommonJS → ESM)
- @automaker/platform (CommonJS → ESM)
- @automaker/utils (CommonJS → ESM)

Benefits:
✅ Consistent module system across all packages
✅ Better tree-shaking and modern bundling support
✅ Native browser support (future-proof)
✅ Fixes E2E CI server startup issues

All tests passing: 632/632 server tests

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

libs/utils/src/prompt-builder.ts

@@ -8,7 +8,7 @@
  * - Supports both vision and non-vision models
  */
 
-import { convertImagesToContentBlocks, formatImagePathsForPrompt } from "./image-handler";
+import { convertImagesToContentBlocks, formatImagePathsForPrompt } from "./image-handler.js";
 
 /**
  * Content that can be either simple text or structured blocks