fix(api/history): include coin_queue in balance read

[TaprootFreak]

Problem

api_remote::history_after_mint_records_mint_row fails against dev-api
on PR #166 (Release: develop -> main):

assertion `left == right` failed
  left: Number(0)
 right: 50000

/api/history returns items[0].amount = 0 for the first mint of a
fresh address, where the wire contract is the credited amount.

Root cause

router::balance_from_account_blob reads only Account.balance — the
settled balance after sends. The mint / receive paths push the credited
coin into coin_queue without touching balance; Account::get_balance()
is the only call that sums both. So history_row_to_item computed
new_balance = 0, prev_balance = 0, amount = 0 for every mint row.

The existing unit test fixture set a.balance directly, which no
production write path produces on the mint or receive path — that hid
the gap until the E2E suite ran against a real commit_mint_tx write.

Fix

• balance_from_account_blob: deserialize, then sum balance + Σ coin_queue.amount (mirrors Account::get_balance()). saturating_add on the untrusted-blob summands.
• history_row_to_item_handles_first_row_with_no_prev_data: docs-only — clarifies that it pins the settled-balance variant (still a valid post-send shape) and points to the queue-only sibling test.
• New test history_row_to_item_balance_from_coin_queue_only in account_node_tests: walks the real mint flow (execute_send_coins + receive_coin) and asserts both balance_from_account_blob directly and the end-to-end history_row_to_item output.

No wire-shape change, no schema change, no migration.

Verification

• cargo fmt --all -- --check: clean
• cargo clippy -p node -p shared -- -D warnings: clean
• cargo build -p node: clean
• Heavy tests deferred to CI.

Unblocks

PR #166 (Release develop -> main).