refactor(legacy): split legacy_shared into cohesive packages

legacy_shared was the junk drawer of the legacy app mode — 37 files
mixing device entities, command infrastructure, UI primitives, generic
formatters, and a duplicate of sf_infrastructure's dio_error_mapper.
Any module needing one piece pulled the whole bag into its graph.

Split it by responsibility, following Mandamiento 4 of Real-World Flutter:

- legacy_ui (new): 6 widget/layout primitives (PageLayout, MenuButton,
  SectionButton, PulsingLocationMarker, RefreshableErrorState,
  WeekDayChips) plus mapStyleProvider — shared UI state that was the
  only reason two modules needed a common package.
- legacy_device_state (expanded 9 → 30): absorbed device entities,
  commands infrastructure (datasource + repo + provider + guard),
  device settings update flow, and the CSV exporter. Now one package
  owns the device domain end-to-end.
- packages/utils: absorbed battery_utils and date_format_utils as pure
  formatters that never belonged in a legacy-scoped package.
- legacy_shared: deleted entirely.

The duplicate dio_error_mapper in legacy_shared is gone; callers now use
the sf_infrastructure version (which was always the superset — it adds
ApiException and the dart:io socket handling).

DeviceEntity note: legacy_device_state keeps its own DeviceEntity (with
int timestamps and typed paymentOptions) separate from sf_shared's
DeviceEntity (String timestamps, untyped paymentOptions). The legacy
one is intentionally not exported from the barrel to avoid the
ambiguous_import collision that legacy_shared quietly hid by never
exporting it in the first place. Unifying the two is a domain-model
refactor out of scope here.

0 cross-module imports remain among legacy feature modules.

pubspec.yaml

@@ -23,9 +23,9 @@ workspace:
   - modules/legacy/modules/legacy_dashboard_shell
   - modules/legacy/modules/location
   - modules/legacy/modules/settings
-  - modules/legacy/packages/legacy_shared
   - modules/legacy/packages/legacy_device_state
   - modules/legacy/packages/legacy_theme
+  - modules/legacy/packages/legacy_ui
   - packages/design_system
   - packages/flutter_treezor_entrust_sdk_bridge
   - packages/flutter_treezor_entrust_sdk_bridge/example