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/index.ts

@@ -10,7 +10,7 @@ export {
   isAuthenticationError,
   classifyError,
   getUserFriendlyErrorMessage,
-} from './error-handler';
+} from './error-handler.js';
 
 // Conversation utilities
 export {
@@ -18,7 +18,7 @@ export {
   normalizeContentBlocks,
   formatHistoryAsText,
   convertHistoryToMessages,
-} from './conversation-utils';
+} from './conversation-utils.js';
 
 // Image handling
 export {
@@ -26,14 +26,14 @@ export {
   readImageAsBase64,
   convertImagesToContentBlocks,
   formatImagePathsForPrompt,
-} from './image-handler';
+} from './image-handler.js';
 
 // Prompt building
 export {
   buildPromptWithImages,
   type PromptContent,
   type PromptWithImages,
-} from './prompt-builder';
+} from './prompt-builder.js';
 
 // Logger
 export {
@@ -41,10 +41,10 @@ export {
   getLogLevel,
   setLogLevel,
   LogLevel,
-} from './logger';
+} from './logger.js';
 
 // File system utilities
 export {
   mkdirSafe,
   existsSafe,
-} from './fs-utils';
+} from './fs-utils.js';