Add landing page, redesign emails, and return updated task on completion

- Integrate landing page into Go app (served at root /)
- Add STATIC_DIR config for static file serving
- Redesign all email templates with modern dark theme styling
- Add app icon to email headers
- Return updated task with kanban_column in completion response
- Update task DTO to include kanban column for client-side state updates

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/config/config.go

@@ -29,6 +29,7 @@ type ServerConfig struct {
 	Debug        bool
 	AllowedHosts []string
 	Timezone     string
+	StaticDir    string // Directory for static landing page files
 }
 
 type DatabaseConfig struct {
@@ -148,6 +149,7 @@ func Load() (*Config, error) {
 			Debug:        viper.GetBool("DEBUG"),
 			AllowedHosts: strings.Split(viper.GetString("ALLOWED_HOSTS"), ","),
 			Timezone:     viper.GetString("TIMEZONE"),
+			StaticDir:    viper.GetString("STATIC_DIR"),
 		},
 		Database: dbConfig,
 		Redis: RedisConfig{
@@ -217,6 +219,7 @@ func setDefaults() {
 	viper.SetDefault("DEBUG", false)
 	viper.SetDefault("ALLOWED_HOSTS", "localhost,127.0.0.1")
 	viper.SetDefault("TIMEZONE", "UTC")
+	viper.SetDefault("STATIC_DIR", "/app/static")
 
 	// Database defaults
 	viper.SetDefault("DB_HOST", "localhost")