♲ Refactor configuration to use viper with context propagation

- Replace global ConfigPath and Overrides with viper-based configuration
- Add viper.New() to create configurable viper instances
- Store viper and unmarshaled Config struct in context for testability
- Add RetrieveFromContext and AddToContext helper functions
- Update files.Append to accept context and retrieve config from it
- Update formatters.Preferred and formatters.New to accept context
- Add PersistentPreRunE in CLI to create and configure viper instance
- Support -c flag for custom config file path
- Support -v flag for config value overrides
- Update all test files to create viper and add to context
- Remove unused config types and load functions
- Add viper as dependency with automatic env var support (MYLOG_*)

cmd/my-log/main.go

@@ -1,5 +1,5 @@
 /*
-Copyright © 2024 Dan Jones <danjones@goodevilgenius.org>
+Copyright © 2026 Dan Jones <danjones@goodevilgenius.org>
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU Affero General Public License as published by
@@ -16,8 +16,12 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 package main
 
-import "codeberg.org/danjones000/my-log/cli"
+import (
+	"context"
+
+	"codeberg.org/danjones000/my-log/cli"
+)
 
 func main() {
-	cli.Execute()
+	cli.Execute(context.Background())
 }