[test] Add tests for logger.ToolsLogger.writeToFile and LogToolsForServer

[github-actions]

Test Coverage Improvement: ToolsLogger.writeToFile & LogToolsForServer

Function Analyzed

• Package: internal/logger
• File: internal/logger/tools_logger.go
• Functions targeted: writeToFile (line 107) and LogToolsForServer (line 141)
• Previous Coverage: writeToFile 63.6% · LogToolsForServer 66.7%
• New Coverage: writeToFile 90.9% · LogToolsForServer 100.0%

Why These Functions?

writeToFile performed an atomic write via a temp-file-plus-rename pattern with three distinct error branches — none of which were exercised by the existing test suite. LogToolsForServer had its warning-log path (triggered when LogTools returns an error) completely untested. Together they had the lowest coverage of any non-trivial functions in the testable packages.

Tests Added

Test	What it covers
TestWriteToFile_Success	Happy-path: temp file written, renamed, original cleaned up, valid JSON on disk
TestWriteToFile_WriteFileFails	os.WriteFile fails → "failed to write temp file" error returned
TestWriteToFile_RenameFails	os.Rename fails (EISDIR — target is a directory) → "failed to rename temp file" error + temp file removed
TestLogToolsForServer_ErrorIsLogged	Global logger pointed at bad path so LogTools errors → log.Printf("WARNING: …") branch hit
TestLogToolsForServer_FallbackSkipsErrors	Logger in fallback mode silently discards without reaching error branch

Coverage Report

Before:  writeToFile 63.6% · LogToolsForServer  66.7%
After:   writeToFile 90.9% · LogToolsForServer 100.0%
```

The remaining ~9% of `writeToFile` is the `json.MarshalIndent` error branch (line 113), which cannot be reached with valid `ToolsData` structs at runtime.

### Test Execution

```
=== RUN   TestWriteToFile_Success
--- PASS: TestWriteToFile_Success (0.00s)
=== RUN   TestWriteToFile_WriteFileFails
--- PASS: TestWriteToFile_WriteFileFails (0.00s)
=== RUN   TestWriteToFile_RenameFails
--- PASS: TestWriteToFile_RenameFails (0.00s)
=== RUN   TestLogToolsForServer_ErrorIsLogged
--- PASS: TestLogToolsForServer_ErrorIsLogged (0.00s)
=== RUN   TestLogToolsForServer_FallbackSkipsErrors
--- PASS: TestLogToolsForServer_FallbackSkipsErrors (0.00s)
PASS
ok  github.com/github/gh-aw-mcpg/internal/logger 0.006s

Full logger package suite: ok github.com/github/gh-aw-mcpg/internal/logger

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