feat(studio): operator QoL — flow runnability, audit grouping, batch approvals, welcome celebration (v0.42.0)

Four UX threads stitched into one commit. Each pulls Studio
toward Stefan's "zero-learning-curve" goal — the feedback
that earned its own memory entry.

1. Flow-Runnability-Indikator
   ─────────────────────────
   The Flows tab now fetches `listFlows` and `listModules`
   in parallel. Each card compares the flow's
   `requiredCapabilities` against the installed-modules'
   capability set; rows with missing modules show a "Needs:
   text.extract@^0" red pill row beneath the path and have
   their Run button greyed out + tooltip
   "Install the missing modules first." Operators stop
   hitting Run → cryptic hub error → frustration.

2. Welcome-Checklist Celebration
   ─────────────────────────────
   Once all four checklist signals flip to done, an
   `_AllDoneCelebration` card replaces the bare
   "All four steps complete" + Hide button. Three concrete
   next-threads with action buttons: "Read the audit log",
   "Set up the daily Today story" (opens the Flows / Today
   doc inline via `_DocReaderSheet`), and "Build your own
   module" (opens the architecture doc). Operator who just
   got set up sees what to do next instead of an empty
   "what now?" feeling.

3. Audit-Page Time-Bucket Headers + Flow-Run Detail
   ────────────────────────────────────────────────
   The flat event list grows tiny "TODAY / YESTERDAY /
   EARLIER THIS WEEK / OLDER" section headers — bucket is
   computed in the operator's local timezone so an event at
   23:55 yesterday in Berlin doesn't end up in "today"
   because UTC happened to spill into a new day.
   Plus: the event-detail dialog gains a "View flow run"
   action when the picked event has a `flow_execution`. It
   opens a drill-down that lists every event in the
   already-fetched 100-event window sharing the same
   execution id, sorted ascending — the operator reads the
   run from step.started top to flow.completed bottom.

4. Approvals-Batch-Aktionen
   ────────────────────────
   Each pending approval card grows a checkbox. When ≥1
   selected, a floating action bar appears at the bottom
   with "N selected · Select all · Clear · Reject all ·
   Approve all". The parent loops sequentially through the
   per-record SDK calls so a partial failure produces
   "X done, Y failed" instead of a confusing all-or-nothing
   rollback. Reject prompts for a reason once and applies
   to the whole picked set.

13 new ARB keys cover the strings the four features
needed. Studio's tests stay green.

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: 0.41.0
+version: 0.42.0
 
 environment:
   sdk: ^3.11.0-200.1.beta