fix(accounts): provision USDF core account for fresh onboards even with a stale cache

[bmc08gt]

Problem

Sending a tip to a freshly-onboarded account failed on both Android and iOS with the server error:

payments to external destinations must be withdrawals

The failure was recipient-specific ("works for some users"), cross-platform, and — tellingly — killing and relaunching the receiver's app fixed it.

Root cause

The tip send path is a legitimate direct send; the OCP server auto-opens the recipient's currency destination (detectAutoOpenPrimaryAccount) only if it recognizes the recipient as an OCP user, which it does purely by the presence of a USDF core-mint PRIMARY (ocp-server owner.go).

On the client, AccountController.ensureCoreAccount (the onboarding gate that's supposed to guarantee that primary) short-circuited on the in-memory accounts cache. That cache still held the previous account's USDF primary after a logout → re-onboard in the same process, so the gate logged USDF core account already present and provisioned nothing — releasing a fresh account to the scanner with no core account server-side (getAccounts returned NOT_FOUND for the new owner). Only a process restart cleared the cache, which is why relaunch "fixed" it.

On-device logs (receiver, fresh onboard, same PID — no relaunch):

[Onboarding] : Access key seen
[Onboarding] : USDF core account already present   <- short-circuited on stale cache
[Onboarding] : releasing to scanner
[RpcLogging] : GetTokenAccountInfosResponse { result=1 }   <- NOT_FOUND for the new owner

Fix

• ensureCoreAccount is now server-authoritative — it always confirms the current owner via getAccounts instead of trusting the local cache, and provisions the USDF primary when absent (checking account type, not just mint), tolerating a race with the reactive account bootstrap.
• onUserLoggedIn clears the cached account list when the account changes, preventing cross-account bleed into all consumers (balances, hasAccountFor, and the onboarding gate).

Tests

AccountControllerTest (8 passing), including new regression coverage:

• ensureCoreAccount ignores a stale cached USDF primary from a prior account
• onUserLoggedIn clears cached accounts when the account changes
• plus success-without-primary / empty / concurrent-open cases.

Verification

Verified on-device: a freshly-onboarded receiver now provisions its USDF core account during onboarding (Provisioning USDF core account (onboarding gate) + an OpenAccountAction for the USDF mint), and receives a direct-send tip on the first attempt with no relaunch.