[log] Add debug logging to GenerateRandomAPIKey in auth/apikey.go (#4002)

## Summary

Adds 3 debug logging calls to `internal/auth/apikey.go` using the
existing package-level logger (`log`, declared in `auth/header.go`).

### Changes

**`internal/auth/apikey.go`** — 3 new `log.Print` / `log.Printf` calls
in `GenerateRandomAPIKey`:

| Location | Log message |
|----------|-------------|
| Function entry | `"Generating random API key"` |
| On error | `"Random API key generation failed: %v"` |
| On success | `"Random API key generated successfully"` |

### Why this file?

`GenerateRandomAPIKey` is called at gateway startup (spec §7.3) whenever
no API key is configured. Logging this lifecycle event helps developers:

- Confirm that key generation occurs when expected
- Diagnose failures in `strutil.RandomHex` (e.g., entropy issues)
- See the startup sequence in `DEBUG=auth:*` output

### Design decisions

- **Reuses existing logger**: `var log = logger.New("auth:header")` is
already declared in the `auth` package. No new logger variable or import
is needed in `apikey.go`.
- **No key exposure**: The log messages confirm generation
success/failure without logging the actual key value.
- **No side effects**: All log arguments are already-evaluated
variables.

### Validation

- `go build ./...` ✅
- `go vet ./...` ✅  
- `go test ./internal/auth/...` ✅ (all tests pass)
- `go test ./...` ✅ (all unit tests pass; pre-existing integration test
failures unrelated to this change)

### Enabling debug output

```bash
DEBUG=auth:* ./awmg --config config.toml
```




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Author: lpcox

internal/auth/apikey.go

@@ -3,16 +3,22 @@ package auth
 import (
 	"fmt"
 
+	"github.com/github/gh-aw-mcpg/internal/logger"
 	"github.com/github/gh-aw-mcpg/internal/strutil"
 )
 
+var logAPIKey = logger.New("auth:apikey")
+
 // GenerateRandomAPIKey generates a cryptographically random API key.
 // Per spec §7.3, the gateway SHOULD generate a random API key on startup
 // if none is provided. Returns a 32-byte hex-encoded string (64 chars).
 func GenerateRandomAPIKey() (string, error) {
+	logAPIKey.Print("Generating random API key")
 	key, err := strutil.RandomHex(32)
 	if err != nil {
+		logAPIKey.Printf("Random API key generation failed: %v", err)
 		return "", fmt.Errorf("failed to generate random API key: %w", err)
 	}
+	logAPIKey.Print("Random API key generated successfully")
 	return key, nil
 }