ui: /settings/notifications list + edit form (3 kinds)

Add settings.html (shell + sub-tab nav + conditional list/edit body),
notifications.html and notification_edit.html (glob stubs), and the
supporting CSS tokens (.ch-row, .ch-icon, .toggle, .kind-grid,
.kind-card, .radio-pip, .test-pill) to input.css. Rebuild styles.css.
Add ui_parse_test.go to catch template regressions at test time.

The kind picker is JS-driven (no full page reload); the enabled toggle
mirrors the existing visual toggle pattern; the test-notification button
uses HTMX and renders the JSON response as a coloured pill client-side.

internal/server/ui/ui_parse_test.go

@@ -0,0 +1,12 @@
+package ui
+
+import "testing"
+
+// TestNewParsesAllTemplates ensures ui.New() can parse every template
+// registered under templates/pages/ without error. Run this after
+// adding or editing any template file.
+func TestNewParsesAllTemplates(t *testing.T) {
+	if _, err := New(); err != nil {
+		t.Fatalf("ui.New() returned error: %v", err)
+	}
+}