feat: add internal/ui prompts + init subcommand

- internal/ui/prompts.go: MultiSelect with huh TUI + WithNonInteractive for tests
- internal/cli/init.go: NewInit cobra command with --from/--no-prompt flags
- internal/cli/init_test.go: TestInitImportWritesCanonical
- internal/cli/root.go: add resolveRoot helper (shared by profile/rollback/show/init)
- go.mod: add github.com/charmbracelet/huh v1.0.0 as direct dep

internal/ui/prompts.go

@@ -0,0 +1,62 @@
+// Package ui provides small interactive prompts and their non-interactive
+// equivalents for tests.
+package ui
+
+import (
+	"fmt"
+
+	"github.com/charmbracelet/huh"
+)
+
+type msOpts struct {
+	nonInteractive []string
+	interactive    bool
+}
+
+// Option configures MultiSelect behaviour.
+type Option func(*msOpts)
+
+// WithNonInteractive bypasses the TUI entirely and returns the given choices.
+// Test code uses this to make MultiSelect deterministic.
+func WithNonInteractive(choices []string) Option {
+	return func(o *msOpts) {
+		o.nonInteractive = choices
+		o.interactive = false
+	}
+}
+
+// MultiSelect prompts the user (or returns the pre-set non-interactive value).
+// Choices passed via WithNonInteractive must all appear in `choices`.
+func MultiSelect(title string, choices []string, opts ...Option) ([]string, error) {
+	o := &msOpts{interactive: true}
+	for _, fn := range opts {
+		fn(o)
+	}
+	if !o.interactive {
+		valid := map[string]bool{}
+		for _, c := range choices {
+			valid[c] = true
+		}
+		for _, c := range o.nonInteractive {
+			if !valid[c] {
+				return nil, fmt.Errorf("choice %q not in %v", c, choices)
+			}
+		}
+		return o.nonInteractive, nil
+	}
+	var picked []string
+	opts2 := make([]huh.Option[string], 0, len(choices))
+	for _, c := range choices {
+		opts2 = append(opts2, huh.NewOption(c, c))
+	}
+	form := huh.NewForm(huh.NewGroup(
+		huh.NewMultiSelect[string]().
+			Title(title).
+			Options(opts2...).
+			Value(&picked),
+	))
+	if err := form.Run(); err != nil {
+		return nil, err
+	}
+	return picked, nil
+}

internal/ui/prompts_test.go

@@ -0,0 +1,18 @@
+package ui
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMultiSelectNonInteractive(t *testing.T) {
+	sel, err := MultiSelect("pick", []string{"a", "b", "c"}, WithNonInteractive([]string{"a", "c"}))
+	assert.NoError(t, err)
+	assert.Equal(t, []string{"a", "c"}, sel)
+}
+
+func TestMultiSelectNonInteractiveInvalidChoice(t *testing.T) {
+	_, err := MultiSelect("pick", []string{"a", "b"}, WithNonInteractive([]string{"z"}))
+	assert.Error(t, err)
+}