feat(studio): Welcome page Phase C — live getting-started checklist (v0.39.0)

Final slice of the Welcome surface. Four steps that prove
the operator has the basic loop wired up; each step is
a live probe against the running hub, no manual ticks.

The four checked signals:

  1. System AI configured
     → `HubService.systemAiStatus().enabled`
  2. Public capability source added
     → `listMcpClients()` returns at least one entry
  3. Text module installed
     → `listModules()` contains a name starting with `text.`
  4. Saved flow run
     → any `flow.completed` event in the last 100 audit
       events

All four probes fire in parallel from `_OnboardingChecklist`'s
`_refresh()`. Failures stay false (catchError) so a hub that
is briefly unreachable doesn't blank the whole row — the
operator hits the explicit Refresh icon to retry.

UX:

- Renders between hero and pillars so the actionable path
  beats the educational content for screen real estate.
- Each row: status icon (○ pending / ✓ done) + title +
  one-line hint pointing the operator at the right Studio
  surface + status pill.
- Done rows strike-through the title and dim it; pending
  rows stay full-strength.
- When all four flip to done, an "All four steps complete"
  footer appears with a `Hide checklist` button. Clicking
  persists `welcome.checklist.dismissed = true` via
  SharedPreferences; the section is gone for good (we don't
  re-nag operators who chose a non-default path).

15 new ARB keys for the section header, body, four rows
plus done/pending pills, all-done footer, dismiss /
refresh / refreshing button labels.

Three-phase plan from `docs/landing-page-design.md` is now
fully shipped: Phase A scaffolding (v0.37.0), Phase B
embedded doc reader (v0.38.0), Phase C live checklist
(v0.39.0).

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_localizations_en.dart

@@ -112,6 +112,59 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Could not load documentation: $error';
   }
 
+  @override
+  String get welcomeChecklistHeader => 'GETTING STARTED';
+
+  @override
+  String get welcomeChecklistBody =>
+      'Four steps to a working hub. Live state — refresh after changing anything.';
+
+  @override
+  String get welcomeChecklistAi => 'Configure System AI';
+
+  @override
+  String get welcomeChecklistAiHint =>
+      'Settings → System AI. Required for the AI search and inline failure explanations.';
+
+  @override
+  String get welcomeChecklistMcp => 'Add a public capability source';
+
+  @override
+  String get welcomeChecklistMcpHint =>
+      'Store → Today hero, or Settings → MCP Clients. DeepWiki and Semgrep are one click each.';
+
+  @override
+  String get welcomeChecklistModule => 'Install a text module';
+
+  @override
+  String get welcomeChecklistModuleHint =>
+      'Store → search \"text\" → Install. Try text.extract for PDFs and DOCX.';
+
+  @override
+  String get welcomeChecklistFlow => 'Run a saved flow';
+
+  @override
+  String get welcomeChecklistFlowHint =>
+      'Flows → pick one → Run. The bundled extract-summarize.yaml is a good first run.';
+
+  @override
+  String get welcomeChecklistAllDone => 'All four steps complete.';
+
+  @override
+  String get welcomeChecklistDismiss => 'Hide checklist';
+
+  @override
+  String get welcomeChecklistRefresh => 'Refresh';
+
+  @override
+  String get welcomeChecklistRefreshing => 'Checking…';
+
+  @override
+  String get welcomeChecklistDone => 'Done';
+
+  @override
+  String get welcomeChecklistTodo => 'Pending';
+
   @override
   String get navDoctor => 'Doctor';