[log] Add debug logging to resolveWasmCacheDir in cmd/flags_logging (#5494)

Adds 3 debug logging calls to `resolveWasmCacheDir` in
`internal/cmd/flags_logging.go` to trace how the WASM compilation cache
directory is resolved at startup.

### Changes

- Log when directory is resolved from the `--wasm-cache-dir` CLI flag
- Log when directory is resolved from the `MCP_GATEWAY_WASM_CACHE_DIR`
environment variable
- Log when directory falls back to the default
(`<log-dir>/wazero-cache`)

### Why This Is Useful

When debugging startup issues or verifying configuration, it's helpful
to know which source (CLI flag, env var, or default) determined the WASM
cache directory. The existing `debugLog` from `root.go` is reused — no
new logger declaration was needed.

Enable via:
```bash
DEBUG=cmd:root ./awmg --config config.toml
```




> Generated by [Go Logger
Enhancement](https://github.com/github/gh-aw-mcpg/actions/runs/25703783871/agentic_workflow)
· ● 6.2M ·
[◷](https://github.com/search?q=repo%3Agithub%2Fgh-aw-mcpg+%22gh-aw-workflow-id%3A+go-logger%22&type=pullrequests)

<!-- gh-aw-agentic-workflow: Go Logger Enhancement, engine: copilot,
version: 1.0.40, model: claude-sonnet-4.6, id: 25703783871, workflow_id:
go-logger, run:
https://github.com/github/gh-aw-mcpg/actions/runs/25703783871 -->

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

Author: lpcox

internal/cmd/flags_logging.go

@@ -29,16 +29,20 @@ func defaultWasmCacheDir(logDir string) string {
 
 func resolveWasmCacheDir(flagChanged bool, flagValue, effectiveLogDir string) string {
 	if trimmed := strings.TrimSpace(flagValue); flagChanged && trimmed != "" {
+		debugLog.Printf("WASM cache dir resolved from CLI flag: %q", trimmed)
 		return trimmed
 	}
 
 	if envValue, exists := os.LookupEnv(wasmCacheDirEnvVar); exists {
 		if trimmed := strings.TrimSpace(envValue); trimmed != "" {
+			debugLog.Printf("WASM cache dir resolved from %s: %q", wasmCacheDirEnvVar, trimmed)
 			return trimmed
 		}
 	}
 
-	return defaultWasmCacheDir(effectiveLogDir)
+	resolved := defaultWasmCacheDir(effectiveLogDir)
+	debugLog.Printf("WASM cache dir resolved from default (logDir=%q): %q", effectiveLogDir, resolved)
+	return resolved
 }
 
 func init() {