Add wallet balance refresh

[hellno]

Summary

Linked issue

Closes #

Definition of Done

All of the following must hold before this PR can merge. Paste the command output as evidence —
do not check a box you have not verified.

• cargo fmt --all --check is clean
• just check is green — clippy -D warnings on both the default config and --features tray
• cargo test --workspace is green
• No new or changed dependencies in Cargo.toml / Cargo.lock (unless explicitly approved in this PR;
  the git GPUI stack is bumped only via just bump-gpui, never hand-edited)
• Any visual/UI change follows DESIGN.md (amber = human, cyan = agent; sidebar/contextual-views IA;
  clear-signing / seed-reveal trust affordances)
• Secrets (seed / key / passphrase) stay in Zeroizing and are never logged or Debug-printed

Evidence (paste command output here)

$ cargo fmt --all --check
# (output)

$ just check
# (output)

$ cargo test --workspace
# (output)

Notes for reviewers