migrate admin forms to inline feedback

Replace put_flash calls with inline feedback for form saves:
- Email settings: "Now send a test email" after saving
- Settings: from address and signing secret saves
- Page editor: save button shows "Saved" checkmark

Inline feedback appears next to save buttons and auto-clears after
3 seconds. Banners (put_flash) remain for page-level outcomes like
deletions, state changes, and async operations.

Task 3 of notification overhaul. Theme editor skipped as it auto-saves.

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

PROGRESS.md

@@ -69,13 +69,13 @@ Based on usability testing (March 2026). Reworks the entire setup flow into a si
 
 ### Notification system overhaul ([plan](docs/plans/notification-overhaul.md))
 
-Replace floating toast/flash messages with inline feedback and persistent top banners. 110+ flash messages across 28 files to migrate.
+Replace floating toast/flash messages with inline feedback and persistent top banners. ~140 flash messages across 28 files to migrate. Inline feedback for form saves, banners for page-level outcomes.
 
 | # | Task | Est | Status |
 |---|------|-----|--------|
-| 1 | Build inline feedback component | 1.5h | planned |
-| 2 | Build persistent top banner component (replaces flash) | 1.5h | planned |
-| 3 | Migrate admin forms to inline feedback (theme, pages, settings, email, providers) | 3h | planned |
+| 1 | Build inline feedback component | 1.5h | done |
+| 2 | Build persistent top banner component (replaces flash) | 1.5h | done |
+| 3 | Migrate admin forms to inline feedback (theme, pages, settings, email, providers) | 3h | in progress |
 | 4 | Migrate remaining admin pages (media, products, activity, newsletter, redirects, nav) | 2h | planned |
 | 5 | Migrate shop pages (cart, contact, checkout, auth) | 2h | planned |
 | 6 | Migrate setup wizard notifications | 1h | planned |