[log] Add debug logging to main.go (#914)

## Summary

Enhanced `main.go` with debug logging to improve troubleshooting and
development visibility.

## Changes Made

Added 7 meaningful debug logging statements:
- **Application lifecycle**: Log at application start and before
executing root command
- **Version string construction**: Log when building version string with
metadata
- **Version determination**: Log whether using ldflags version or
defaulting to 'dev'
- **Git commit tracking**: Log commit source (ldflags vs build info) and
extraction process
- **Build metadata**: Log commit hash found in build info

## Technical Details

- Added logger import: `"github.com/github/gh-aw-mcpg/internal/logger"`
- Added logger declaration: `var log = logger.New("main:main")`
- All logging follows project guidelines from AGENTS.md:
  - Uses correct naming convention (`main:main`)
  - No side effects in log arguments
  - Meaningful messages for debugging
  - Focused on entry points and control flow

## Testing

To see the new debug logs in action:

``````bash
DEBUG=main:* ./awmg --version
``````

This will show the version string construction process with all
intermediate steps.

## Quality Checklist

- ✅ Exactly 1 file modified (focused, single-file PR)
- ✅ No test files modified
- ✅ Logger naming follows `pkg:filename` convention
- ✅ Logger arguments don't compute anything or cause side effects
- ✅ Logging messages are meaningful and helpful
- ✅ No duplicate logging with existing logs
- ✅ Import statements properly formatted


> AI generated by [Go Logger
Enhancement](https://github.com/github/gh-aw-mcpg/actions/runs/21946284845)

<!-- gh-aw-workflow-id: go-logger -->

Author: lpcox

main.go

@@ -6,16 +6,23 @@ import (
 	"strings"
 
 	"github.com/github/gh-aw-mcpg/internal/cmd"
+	"github.com/github/gh-aw-mcpg/internal/logger"
 )
 
+var log = logger.New("main:main")
+
 func main() {
+	log.Print("Starting MCP Gateway application")
+	
 	// Build version string with metadata
 	versionStr := buildVersionString()
+	log.Printf("Built version string: %s", versionStr)
 
 	// Set the version for the CLI
 	cmd.SetVersion(versionStr)
 
 	// Execute the root command
+	log.Print("Executing root command")
 	cmd.Execute()
 }
 
@@ -25,26 +32,32 @@ const (
 
 // buildVersionString constructs a detailed version string with build metadata
 func buildVersionString() string {
+	log.Print("Building version string from build metadata")
 	var parts []string
 
 	// Add main version
 	if Version != "" {
+		log.Printf("Using version from ldflags: %s", Version)
 		parts = append(parts, Version)
 	} else {
+		log.Print("No version set, using 'dev'")
 		parts = append(parts, "dev")
 	}
 
 	// Add git commit if available
 	if GitCommit != "" {
+		log.Printf("Using git commit from ldflags: %s", GitCommit)
 		parts = append(parts, fmt.Sprintf("commit: %s", GitCommit))
 	} else if buildInfo, ok := debug.ReadBuildInfo(); ok {
+		log.Print("Extracting commit hash from build info")
 		// Try to extract commit from build info if not set via ldflags
 		for _, setting := range buildInfo.Settings {
 			if setting.Key == "vcs.revision" {
 				commitHash := setting.Value
 				if len(commitHash) > shortHashLength {
 					commitHash = commitHash[:shortHashLength] // Short hash
 				}
+				log.Printf("Found commit hash in build info: %s", commitHash)
 				parts = append(parts, fmt.Sprintf("commit: %s", commitHash))
 				break
 			}