feat(config): support cli config path and nested config

Adds -config CLI flag to main.go. Moves ParseLogLevel to internal/config. Adds ServerConfig nested struct to Config and corresponding tests for yaml/env overrides.

internal/config/config_test.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"log/slog"
 	"os"
 	"path/filepath"
 	"testing"
@@ -13,6 +14,9 @@ func TestLoad(t *testing.T) {
 	
 	yamlContent := []byte(`
 log_level: "info"
+server:
+  host: "localhost"
+  port: 8080
 `)
 	if err := os.WriteFile(configFile, yamlContent, 0644); err != nil {
 		t.Fatalf("failed to write temp config file: %v", err)
@@ -26,11 +30,23 @@ log_level: "info"
 		if cfg.LogLevel != "info" {
 			t.Errorf("expected LogLevel 'info', got '%s'", cfg.LogLevel)
 		}
+		if cfg.Server.Host != "localhost" {
+			t.Errorf("expected Server.Host 'localhost', got '%s'", cfg.Server.Host)
+		}
+		if cfg.Server.Port != 8080 {
+			t.Errorf("expected Server.Port 8080, got %d", cfg.Server.Port)
+		}
 	})
 
 	t.Run("Override from Env", func(t *testing.T) {
 		os.Setenv("TEST_LOG_LEVEL", "debug")
-		defer os.Unsetenv("TEST_LOG_LEVEL")
+		os.Setenv("TEST_SERVER_PORT", "9090")
+		os.Setenv("TEST_SERVER_HOST", "0.0.0.0")
+		defer func() {
+			os.Unsetenv("TEST_LOG_LEVEL")
+			os.Unsetenv("TEST_SERVER_PORT")
+			os.Unsetenv("TEST_SERVER_HOST")
+		}()
 
 		cfg, err := Load(configFile, "TEST")
 		if err != nil {
@@ -39,5 +55,34 @@ log_level: "info"
 		if cfg.LogLevel != "debug" {
 			t.Errorf("expected LogLevel 'debug', got '%s'", cfg.LogLevel)
 		}
+		if cfg.Server.Port != 9090 {
+			t.Errorf("expected Server.Port 9090, got %d", cfg.Server.Port)
+		}
+		if cfg.Server.Host != "0.0.0.0" {
+			t.Errorf("expected Server.Host '0.0.0.0', got '%s'", cfg.Server.Host)
+		}
 	})
 }
+
+func TestParseLogLevel(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected slog.Level
+	}{
+		{"debug", slog.LevelDebug},
+		{"DEBUG", slog.LevelDebug},
+		{"info", slog.LevelInfo},
+		{"warn", slog.LevelWarn},
+		{"error", slog.LevelError},
+		{"unknown", slog.LevelInfo},
+		{"", slog.LevelInfo},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			if got := ParseLogLevel(tt.input); got != tt.expected {
+				t.Errorf("ParseLogLevel(%q) = %v, want %v", tt.input, got, tt.expected)
+			}
+		})
+	}
+}