Add config package: TOML loading with env overrides

- Base type with standard sections (Server, Database, MCIAS, Log)
- Duration wrapper type for TOML string→time.Duration decoding
- Generic Load[T] with TOML parse, reflection-based env overrides,
  defaults, required field validation, optional Validator interface
- Env overrides: PREFIX_SECTION_FIELD for string, duration, bool,
  []string (comma-separated)
- WebConfig exported for services with web UIs (not embedded in Base)
- 16 tests covering full/minimal configs, defaults, env overrides,
  validation, error cases

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

go.mod

@@ -2,7 +2,10 @@ module git.wntrmute.dev/kyle/mcdsl
 
 go 1.25.7
 
-require modernc.org/sqlite v1.47.0
+require (
+	github.com/pelletier/go-toml/v2 v2.3.0
+	modernc.org/sqlite v1.47.0
+)
 
 require (
 	github.com/dustin/go-humanize v1.0.1 // indirect