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.

web/templates/pages/notification_edit.html

@@ -0,0 +1,9 @@
+{{/* notification_edit.html — rendered by handleUINotificationEditGet/Post via Render("settings", …).
+     This file exists so the glob-discovered page registry includes it cleanly.
+     The actual edit form lives in settings.html's notification_edit_form block. */}}
+{{define "title"}}Edit Channel · Settings · restic-manager{{end}}
+{{define "content"}}
+{{/* This page is served under the "settings" renderer key; this file is a
+     placeholder discovered by the glob so ui.New() registers "notification_edit"
+     as a valid page. Handlers do not call Render("notification_edit", …) directly. */}}
+{{end}}