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_de.arb

@@ -33,6 +33,22 @@
   "welcomeDocClose": "Schließen",
   "welcomeDocFailedToLoad": "Doku konnte nicht geladen werden: {error}",
   "@welcomeDocFailedToLoad": { "placeholders": { "error": { "type": "String" } } },
+  "welcomeChecklistHeader": "ERSTE SCHRITTE",
+  "welcomeChecklistBody": "Vier Schritte zu einem funktionierenden Hub. Live-Zustand — nach jeder Änderung aktualisieren.",
+  "welcomeChecklistAi": "System-AI konfigurieren",
+  "welcomeChecklistAiHint": "Einstellungen → System-AI. Wird für die KI-Suche und Fehlererklärungen gebraucht.",
+  "welcomeChecklistMcp": "Öffentliche Capability-Quelle hinzufügen",
+  "welcomeChecklistMcpHint": "Store → Today-Hero, oder Einstellungen → MCP-Clients. DeepWiki und Semgrep sind je ein Klick.",
+  "welcomeChecklistModule": "Ein Text-Modul installieren",
+  "welcomeChecklistModuleHint": "Store → nach „text\" suchen → Installieren. text.extract für PDFs und DOCX ist ein guter Start.",
+  "welcomeChecklistFlow": "Einen gespeicherten Flow starten",
+  "welcomeChecklistFlowHint": "Flows → einen wählen → Starten. Der mitgelieferte extract-summarize.yaml ist ein guter erster Lauf.",
+  "welcomeChecklistAllDone": "Alle vier Schritte erledigt.",
+  "welcomeChecklistDismiss": "Checkliste ausblenden",
+  "welcomeChecklistRefresh": "Aktualisieren",
+  "welcomeChecklistRefreshing": "Prüfe…",
+  "welcomeChecklistDone": "Erledigt",
+  "welcomeChecklistTodo": "Offen",
   "navDoctor": "Diagnose",
   "navModules": "Module",
   "navStore": "Store",