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>

pubspec.yaml

@@ -1,7 +1,7 @@
 name: fai_studio
 description: "F∆I Studio — desktop GUI for the F∆I hub"
 publish_to: 'none'
-version: 0.38.0
+version: 0.39.0
 
 environment:
   sdk: ^3.11.0-200.1.beta