chore(ui): tear out the v1 UI behind the newUI flag

[bmc08gt]

Follow-up to #1286, which flipped FeatureFlag.NewUi to launched. With the flag
permanently on, every isNewUi branch had exactly one live side — this removes the
flag and collapses those branches, then deletes the v1 surfaces that are stranded
once the branch is gone.

Removed

• FeatureFlag.NewUi and FeatureFlag.NavBar (the v1 nav-bar config flag),
  plus the Labs "Nav Bar" settings screen that edited it.
• The v1 scanner chrome — DecorView, ScannerDecorItem, ScannerNavigationBar,
  LongPressDraggable, NavBarConfig, GiveButtonLabel. The v2 nav bar is a single
  persistent overlay hoisted to the app root; none of this had a caller left.
• apps/flipcash/features/home — the v1 home host. Dropped from settings.gradle.kts.
• The v1 balance surface (BalanceScreen, BalanceScreenContent, CashReservesRow)
  and the v1 currency-info sections (TokenBalance, TokenDetails), superseded by the
  wallet card deck and CurrencyInfoContentV2.
• CurrencyCreatorUpsellCard — the creator promo is a wallet action tile now.

Net: 114 files, +826 / −3969.

UI tests

The Maestro suite and the macrobenchmark still drove v1 affordances — a
"Tips"/"Discover"/"Cash" tab row, a menu_button, a swipe-down sheet dismissal — so
they are retargeted to the v2 tab model rather than left to rot:

• NavigationBar tabs are tagged nav_scanner / nav_wallet / nav_chats /
  nav_tipcard, and helpers/close_open_sheet.yaml unwinds to the scanner tab
  (tabs are replaced on one root back stack, so Back never unwinds between them).
• SwapStep.Entry is explicitly tagged swap_screen. buy.yaml / sell.yaml already
  anchored on that id, but nothing ever emitted it — the derived id is entry_screen.
• CurrencyInfoExpansion carries the token_info_screen anchor too: in v2 a wallet card
  expands as an overlay rather than pushing AppRoute.Token.Info, so the flows would
  otherwise lose their anchor on the most common path into currency info.
• The chats list is tagged chat_list.
• buy.yaml / sell.yaml follow v2 swap semantics: there is no "Sell" (liquidating is a
  Convert into Dollars), "Buy" is "Get" and is only offered on a currency you do not
  hold, and the funding currency is picked inline rather than as a pushed step.
• Give flows enter through Wallet → currency → Give, and cancelling a bill returns to
  currency info, not the scanner.
• BaselineProfileGenerator journeys switch tabs by resource id instead of tapping v1
  labels; sendChatJourney (which entered an unbuilt module via a "Send" tab) becomes a
  chats-tab journey.

Running the suite end-to-end then turned up entry points that had moved with the tab
rework rather than with this teardown:

• Every flow started from scanner_screen, which is no longer where login lands
  (homeRoute = AppRoute.Sheets.Wallet).
• Add Money and Withdraw Money are wallet action tiles now, at the bottom of a
  scrollable list, so each entry needs a scrollUntilVisible — as do Discover
  Currencies and Create a Currency, which were already tiles.
• Log Out moved from My Account to Advanced; App Settings is gone entirely
  (navigate_to_app_settings.yaml and its screenshot leg with it).
• Three flows were pinned to positions in live data. buy.yaml assumed leaderboard row 0
  offers "Get", which it only does for a currency the account does not already hold;
  blocking.yaml and tip_chat.yaml took chat row 0, which is the account's own
  self-tip chat. They select by name now.