fix(deps): Mark BurntSushi/toml as direct dependency (GH#749)

The toml package is imported directly in formula.go and
internal/formula/parser.go but was incorrectly marked as
indirect. This caused Nix builds to fail with vendor
inconsistency errors.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

go.mod

@@ -5,6 +5,7 @@ go 1.24.0
 toolchain go1.24.11
 
 require (
+	github.com/BurntSushi/toml v1.6.0
 	github.com/anthropics/anthropic-sdk-go v1.19.0
 	github.com/charmbracelet/huh v0.8.0
 	github.com/charmbracelet/lipgloss v1.1.0
@@ -22,7 +23,6 @@ require (
 )
 
 require (
-	github.com/BurntSushi/toml v1.6.0 // indirect
 	github.com/atotto/clipboard v0.1.4 // indirect
 	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
 	github.com/catppuccin/go v0.3.0 // indirect