Pin XLM to top of token list and apply value sort to Send flow

[piyalbasu]

What problem does your feature solve?

Follow-up feedback on #2227 (sort balances by USD value) from Emir Ayral:

1. XLM is currently sorted by USD amount like any other token. For a Stellar wallet, XLM is the native asset and should always be the first token in the list regardless of value.
2. The Send flow's token picker is still sorted alphabetically — it didn't get the value-sort change applied in Balances should be ordered by value #2227.

What would you like to see?

• Token / balance list: sort by USD value, but always pin XLM to the top.
• Send flow token picker: same ordering as the balance list (sort by USD value, XLM pinned to top).

What alternatives are there?

• Keep XLM in value-sorted position (current behavior) — rejected by feedback.
• Sort Send picker independently — inconsistent UX.

Context

Slack thread: https://stellarfoundation.slack.com/archives/C03347FNAHK/p1779982000509779