refactor(ui): one canonical segment control (ChainSegments) everywhere

The same single-select choice pattern appeared as four widgets:
audit's hover pills, the store's SegmentedButton, the store filter
dialog's ChoiceChips, and the approvals TabBar (usertest finding
#14 / night-log decision 'pill segment as canon'). The audit
pattern is promoted to a shared ChainSegments widget (optional
icons, hover, selected border, button+selected semantics) and all
four sites use it; approvals switches lists via IndexedStack so
both stay alive and switching does not refetch.

Guard per the no-bugfix-without-a-guard rule: widget tests for
selection + semantics, plus a canon sweep that bans
TabBar/TabBarView/TabController/SegmentedButton/ChoiceChip from
lib/ (comments exempt). Deliberately out of scope: the flow
editor's Graph/Text/Run tabs live in the separate editor package.
Studio 0.75.0; guide images regenerated, dark + light verified.

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

lib/data/about_info.dart

@@ -4,7 +4,7 @@
 
 /// Studio's own build version. Bump on every UI release so the
 /// running app self-identifies.
-const String kStudioVersion = '0.74.0';
+const String kStudioVersion = '0.75.0';
 
 const String kProductName = 'Ch∆In Studio';
 const String kVendorName = 'Flemming.AI (F∆I)';