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/git-utils/src/index.ts

@@ -8,13 +8,13 @@ export {
   BINARY_EXTENSIONS,
   GIT_STATUS_MAP,
   type FileStatus,
-} from './types';
+} from './types.js';
 
 // Export status utilities
 export {
   isGitRepo,
   parseGitStatus,
-} from './status';
+} from './status.js';
 
 // Export diff utilities
 export {
@@ -23,4 +23,4 @@ export {
   listAllFilesInDirectory,
   generateDiffsForNonGitDirectory,
   getGitRepositoryDiffs,
-} from './diff';
+} from './diff.js';