docs(batch): document BatchTranslationService re-initialization investigation (Issue #13)

Investigated potential re-initialization issue in BatchTranslationService.

Findings:
- Analyzed pLimit instance creation on every translateFiles() call
- Confirmed current implementation is CORRECT and follows best practices
- Creating new pLimit per batch provides necessary isolation
- Prevents queue mixing between different batch operations
- Service is stateless with no persistent state between calls
- All 39 batch translation tests pass

Conclusion:
- No code changes needed
- Current implementation is correct
- Issue was either already fixed or false positive from original review
- Each batch operation correctly gets its own pLimit queue

Technical Details:
- pLimit created at line 81 in translateFiles()
- Intentional design for isolation, not a bug
- No mutable state persists between calls
- Concurrency setting properly validated in constructor (1-100)

Location: src/services/batch-translation.ts:81

Author: sjsyrek

CHANGELOG.md

@@ -110,6 +110,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - **Example Attack Prevented**: User creating symlink to `/etc/passwd` and attempting to translate it
   - Location: `src/cli/commands/translate.ts:118-149` (translate method with lstatSync check)
 
+### Changed
+- **Code Quality Review: BatchTranslationService** - Investigated re-initialization concern (Issue #13)
+  - Analyzed pLimit instance creation in translateFiles() method
+  - Confirmed current implementation is CORRECT and intentional
+  - Creating new pLimit per batch operation provides proper isolation
+  - Prevents queue mixing between different batch operations
+  - Service is stateless with no mutable state between calls
+  - All 39 tests pass, no bugs identified
+  - **Conclusion**: No changes needed - current code follows best practices
+  - **Technical Detail**: Each batch operation gets its own pLimit queue for isolation
+  - Location: `src/services/batch-translation.ts:81` (pLimit instance creation)
+
 ### Refactoring
 - **Dead Code Removal: Undefined Marker** - Cleaned up unreachable code (Issue #7)
   - Removed undefined marker check from CacheService.get() method