fix(tokens): correct non USD Phantom add-money flow

[bmc08gt]

Summary

Fixes the Add money via Phantom flow, which was broken for non-USD (e.g. INR) users and mis-navigated on the buy-shortfall path. Found and verified on-device with the app set to INR.

Changes

• Currency mislabel (the deposit failure). The Phantom confirm path forced exchange.rateForUsd(), so the entered amount (in the user's selected currency) was labelled USD — e.g. ₹500 treated as $500. compute() then skipped the FX conversion and produced an underlyingTokenAmount ~83× too large, so checkBalances rejected the deposit as InsufficientUsdc (surfacing at getTokenAccountBalance). Now uses exchange.preferredRate.

• Unlocalized max hint. The "Enter up to X" / over-max hint used a USD-denominated max while the user typed in their local currency. maxAmountFlow now converts the token balance to the preferred currency, so the hint and the over-max comparison agree with the entry field.

• Stranded on the connect prompt (buy-shortfall path). purchaseMethodController.selections is a hot flow with two collectors. The PhantomWallet branch lacked the amount-less-selection guard that CoinbaseOnRamp already had, so tapping Phantom in the deposit sheet double-fired PhantomSelected and navigated the buy flow to PhantomConnect — which reappeared after the nested add-money flow finished. Hoisted the purchaseAmount guard so amount-less deposit-sheet selections are ignored.

• Returned one screen short. The buy-shortfall add-money route stacked on top of the buy flow, so completion popped back to the amount-to-buy step. The OpenScreen handler now replaces the buy flow, so finishing the top-up returns to the token screen (origin) — matching add-money launched directly from the token screen. Note: this abandons the in-progress buy (re-tap Buy with the new balance).

• Processing is terminal. The two Phantom→Processing handlers use replaceStack(listOf(Processing)) so leaving Processing exits the flow rather than surfacing buried connect/confirm steps. Added InnerFlowNavigatorTest cases covering the back-stack behavior (the forward-slide animation is preserved — nav3 treats a root swap as a forward navigation).

Test plan

• :ui:navigation:testDebugUnitTest --tests InnerFlowNavigatorTest — green (9/9).
• On-device (device set to INR): buy hint shows ₹; buy Moony → over-hint amount → Add Money → Phantom → completes and returns to the Moony token-info screen (previously stranded on the connect prompt, then one screen short). Verified by the reporter.