feat(wallet): unified recent activity on the wallet screen

[bmc08gt]

Summary

Add a cross-token Recent activity preview to the wallet, backed by the new :shared:transaction-history presentation layer.

Stacked on #1213 — review/merge that first. This PR's diff is only the feature commit.

• Presentation: ActivityFeedCoordinator + TransactionItemMapper produce presentation-ready TransactionListItem (avatar, signed amount, type-aware title); ActivityFeedRow renders it.
• Titles: "Tipped X" / "Received Tip From X" (counterparty), "Purchased/Sold <token>" (token name), "Added Money" for USDF buys. Server {0} placeholders still take precedence.
• Wallet preview: bounded to the last 3, held in WalletViewModel.State via a non-paged recentTransactions(limit); the paged recentTransactions() is retained for the future full-history dive-in.
• Resolution: counterparty profiles resolve from the user_profiles cache with async resolve-on-miss + resolve-on-fetch back-fill (in-flight de-duped); tokens resolve cache-only via TokenMetadataProvider.observeTokenCache() to avoid per-item network churn in the paging transform.
• Reactive DB: observeProfiles()/observeRecent() react to a new FlipcashDatabase.observeInstance() signal instead of capturing a null per-user DB at singleton construction.
• Persistence: raw text + textSubstitutions on messages (DB 26→27); MessageDao.observeRecent(limit).
• Freeze fix: row key is the full message-id hex (ID.uuid is null for non-16-byte ids, which collapsed every row to key "null" and wedged the LazyColumn under the shared-transition lookahead).
• Cards: TokenCardStack collapses into the deck then scrolls off with the list (scroll read in the placement phase to avoid re-measuring the cards).
• Misc: rename BalanceViewModel → WalletViewModel; extract shared UserProfileDomainMappers; gate scanner decor behind the NewUi flag.

Test Plan

• :shared:transaction-history unit tests pass (title/avatar mapping incl. Added Money, received-tip, bought/sold)
• :features:balance + :shared:persistence:sources unit tests pass
• Wallet shows 3 recent rows; avatars + names resolve live; buys/tips/deposits titled correctly
• Scroll: cards collapse then scroll off; no freeze on tip rows