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.dart

@@ -278,6 +278,102 @@ abstract class AppLocalizations {
   /// **'Could not load documentation: {error}'**
   String welcomeDocFailedToLoad(String error);
 
+  /// No description provided for @welcomeChecklistHeader.
+  ///
+  /// In en, this message translates to:
+  /// **'GETTING STARTED'**
+  String get welcomeChecklistHeader;
+
+  /// No description provided for @welcomeChecklistBody.
+  ///
+  /// In en, this message translates to:
+  /// **'Four steps to a working hub. Live state — refresh after changing anything.'**
+  String get welcomeChecklistBody;
+
+  /// No description provided for @welcomeChecklistAi.
+  ///
+  /// In en, this message translates to:
+  /// **'Configure System AI'**
+  String get welcomeChecklistAi;
+
+  /// No description provided for @welcomeChecklistAiHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Settings → System AI. Required for the AI search and inline failure explanations.'**
+  String get welcomeChecklistAiHint;
+
+  /// No description provided for @welcomeChecklistMcp.
+  ///
+  /// In en, this message translates to:
+  /// **'Add a public capability source'**
+  String get welcomeChecklistMcp;
+
+  /// No description provided for @welcomeChecklistMcpHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Store → Today hero, or Settings → MCP Clients. DeepWiki and Semgrep are one click each.'**
+  String get welcomeChecklistMcpHint;
+
+  /// No description provided for @welcomeChecklistModule.
+  ///
+  /// In en, this message translates to:
+  /// **'Install a text module'**
+  String get welcomeChecklistModule;
+
+  /// No description provided for @welcomeChecklistModuleHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Store → search \"text\" → Install. Try text.extract for PDFs and DOCX.'**
+  String get welcomeChecklistModuleHint;
+
+  /// No description provided for @welcomeChecklistFlow.
+  ///
+  /// In en, this message translates to:
+  /// **'Run a saved flow'**
+  String get welcomeChecklistFlow;
+
+  /// No description provided for @welcomeChecklistFlowHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Flows → pick one → Run. The bundled extract-summarize.yaml is a good first run.'**
+  String get welcomeChecklistFlowHint;
+
+  /// No description provided for @welcomeChecklistAllDone.
+  ///
+  /// In en, this message translates to:
+  /// **'All four steps complete.'**
+  String get welcomeChecklistAllDone;
+
+  /// No description provided for @welcomeChecklistDismiss.
+  ///
+  /// In en, this message translates to:
+  /// **'Hide checklist'**
+  String get welcomeChecklistDismiss;
+
+  /// No description provided for @welcomeChecklistRefresh.
+  ///
+  /// In en, this message translates to:
+  /// **'Refresh'**
+  String get welcomeChecklistRefresh;
+
+  /// No description provided for @welcomeChecklistRefreshing.
+  ///
+  /// In en, this message translates to:
+  /// **'Checking…'**
+  String get welcomeChecklistRefreshing;
+
+  /// No description provided for @welcomeChecklistDone.
+  ///
+  /// In en, this message translates to:
+  /// **'Done'**
+  String get welcomeChecklistDone;
+
+  /// No description provided for @welcomeChecklistTodo.
+  ///
+  /// In en, this message translates to:
+  /// **'Pending'**
+  String get welcomeChecklistTodo;
+
   /// No description provided for @navDoctor.
   ///
   /// In en, this message translates to: