feat(13-02): multi-class ButtonClass() + Icon field + buttonType helper in button.templ

- ButtonClass() now emits "ui-button ui-button-solid ui-button-default ui-button-md"
- Ghost variant special case: "ui-button ui-button-ghost ui-button-md" (tone omitted)
- button.templ: added Icon string field to ButtonProps, replaced inline btnType with buttonType() helper
- ui_test.go: updated TestButton_DefaultSolidMD to multi-class slice assertions
- ui_test.go: updated TestButtonClass_String and TestButtonClass_GhostVariant expectations
- All 18 ui package tests pass

backend/internal/web/ui/button.templ

@@ -3,21 +3,21 @@ package ui
 // ButtonProps is the input to the Button templ component.
 //
 // Type defaults to "button" when empty. Attrs is a pass-through for arbitrary
-// attributes (notably hx-* HTMX attributes).
+// attributes (notably hx-* HTMX attributes). Icon is a named icon key that
+// will be rendered via UIIcon when Plan 04 wires up icon_button.templ.
 type ButtonProps struct {
 	Label   string
 	Variant ButtonVariant
 	Tone    ButtonTone
 	Size    Size
 	Type    string
+	Icon    string
 	Attrs   templ.Attributes
 }
 
 templ Button(props ButtonProps) {
-	{{ btnType := props.Type }}
-	if btnType == "" {
-		{{ btnType = "button" }}
-	}
-	{{ class := ButtonClass(props.Variant, props.Tone, props.Size) }}
-	<button type={ btnType } class={ class } { props.Attrs... }>{ props.Label }</button>
+	<button type={ buttonType(props.Type) } class={ ButtonClass(props.Variant, props.Tone, props.Size) } { props.Attrs... }>
+		// UIIcon added in Plan 04 — Icon field present, rendering wired when UIIcon exists
+		{ props.Label }
+	</button>
 }

backend/internal/web/ui/ui_test.go

@@ -23,9 +23,16 @@ func render(t *testing.T, ctx context.Context, c templ.Component) string {
 func TestButton_DefaultSolidMD(t *testing.T) {
 	out := render(t, context.Background(), Button(ButtonProps{Label: "Fetch server time"}))
 
-	wantClass := `class="ui-button ui-button-solid-default-md"`
-	if !strings.Contains(out, wantClass) {
-		t.Errorf("output missing class %q\ngot: %s", wantClass, out)
+	// Plan 02: multi-class assertions (one check per class token)
+	for _, wantClass := range []string{
+		`ui-button`,
+		`ui-button-solid`,
+		`ui-button-default`,
+		`ui-button-md`,
+	} {
+		if !strings.Contains(out, wantClass) {
+			t.Errorf("output missing class %q\ngot: %s", wantClass, out)
+		}
 	}
 	if !strings.Contains(out, "Fetch server time") {
 		t.Errorf("output missing label literal; got: %s", out)
@@ -102,7 +109,7 @@ func TestBadge_ZeroValueDefaultsToInfo(t *testing.T) {
 
 func TestButtonClass_String(t *testing.T) {
 	got := ButtonClass(ButtonVariantDefault, ButtonToneSolid, SizeMD)
-	want := "ui-button ui-button-solid-default-md"
+	want := "ui-button ui-button-solid ui-button-default ui-button-md"
 	if got != want {
 		t.Errorf("ButtonClass = %q; want %q", got, want)
 	}
@@ -142,11 +149,10 @@ func TestButtonVariantGhost_Normalizer(t *testing.T) {
 
 func TestButtonClass_GhostVariant(t *testing.T) {
 	got := ButtonClass(ButtonVariantGhost, ButtonToneSolid, SizeMD)
-	// ButtonClass uses the compound format (ui-button-{tone}-{variant}-{size}) preserved
-	// from Phase 1 — Plan 02 migrates it to multi-class. Ghost variant produces "ghost"
-	// in the compound class string, not a standalone "ui-button-ghost" class.
-	if !strings.Contains(got, "ghost") {
-		t.Errorf("ButtonClass(Ghost, Solid, MD) = %q; want to contain \"ghost\"", got)
+	// Plan 02: ghost variant omits the tone class and emits "ui-button-ghost" standalone.
+	want := "ui-button ui-button-ghost ui-button-md"
+	if got != want {
+		t.Errorf("ButtonClass(Ghost, Solid, MD) = %q; want %q", got, want)
 	}
 }
 

backend/internal/web/ui/variants.go

@@ -152,12 +152,18 @@ func NormalizedSpacingStep(step SpacingStep) SpacingStep {
 // are normalized before assembly so callers can pass zero values safely.
 //
 // Example: ButtonClass(ButtonVariantDefault, ButtonToneSolid, SizeMD) ==
-// "ui-button ui-button-solid-default-md".
+// "ui-button ui-button-solid ui-button-default ui-button-md".
+//
+// Ghost variant is a special case: the tone class is omitted and "ui-button-ghost"
+// is emitted as a standalone modifier.
 func ButtonClass(variant ButtonVariant, tone ButtonTone, size Size) string {
 	v := NormalizedButtonVariant(variant)
-	t := NormalizedButtonTone(tone)
 	s := NormalizedSize(size)
-	return "ui-button ui-button-" + string(t) + "-" + string(v) + "-" + string(s)
+	if v == ButtonVariantGhost {
+		return "ui-button ui-button-ghost ui-button-" + string(s)
+	}
+	t := NormalizedButtonTone(tone)
+	return "ui-button ui-button-" + string(t) + " ui-button-" + string(v) + " ui-button-" + string(s)
 }
 
 // BadgeClass assembles the deterministic class string for a Badge.