Refine Material surfaces and add local group search (4.1.0)

[seenu-k]

Group rows had become difficult to distinguish from the page, especially with wallpaper colors. Restore connected groups with rounded outer ends, use the softer surfaceContainerHigh role consistently, and make the cover artwork clearer in light mode while preserving the current names, summaries and avatars.

Add local group search through the standard Material SearchAnchor. It searches expense descriptions and payment notes across currencies using the existing SQLite FTS5 index, displays explicit currency codes, and opens the correct editor. Search, People and Settle up remain visible; Refresh moves into More on narrow web screens. Insights keeps its own filters, with controller synchronization fixing both clear actions and restored query text.

The wider interaction pass protects unsaved expense/payment drafts with the standard discard dialog, makes the whole export row actionable, and keeps the export sheet usable with large text. Payer and split sections use outlined Material cards. Refresh store artwork and bump 4.0.0 to 4.1.0 with cider bump minor and cider release.

Validation:

• 207 presentation and database search tests passed, including clear/reset, query restoration, live results, payment/expense navigation, access loss, large text and keyboard layouts.
• 11 toolbar/sync tests passed in Chrome, including the narrow offline toolbar.
• Dart analysis and the repository formatting gate passed.
• Release notes, Play metadata and artwork provenance tests passed; regenerated artwork passes tool/store_artifacts.dart --check.
• Reviewed actual light/dark phone and desktop Flutter renders. Physical handset and screen-reader testing were not performed in this pass.

No dependency, backend, API, database-schema or migration changes.