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/platform/src/index.ts

@@ -20,7 +20,7 @@ export {
   getCredentialsPath,
   getProjectSettingsPath,
   ensureDataDir,
-} from './paths';
+} from './paths.js';
 
 // Subprocess management
 export {
@@ -28,7 +28,7 @@ export {
   spawnProcess,
   type SubprocessOptions,
   type SubprocessResult,
-} from './subprocess';
+} from './subprocess.js';
 
 // Security
 export {
@@ -37,4 +37,4 @@ export {
   isPathAllowed,
   validatePath,
   getAllowedPaths,
-} from './security';
+} from './security.js';