test(wallet): add #[ignore]d live-mainnet integration test for control.wallet.balance (#1959)

[MichaelTaylor3d]

What changed

Closes DIG-Network/dig_ecosystem#1959.

control.wallet.balance (shipped in #1851, rate-bounded in #1957) had a live-mainnet e2e gap: the existing live test (live_funds_dev_tip_broadcasts_and_confirms) covers a $DIG spend, not the balance read. This adds live_wallet_balance_reads_a_funded_address to crates/dig-node-service/tests/live_funds_tip_e2e.rs, reusing that file's harness and gating conventions.

• #[ignore] + env-gated (DIG_LIVE_FUNDS_TEST=1 + DIG_TEST_WALLET_MNEMONIC), mirroring the sibling spend test — so a normal cargo test, and even a bare cargo test -- --ignored, does not touch mainnet without the explicit opt-in. CI never runs it live (both tests report ignored).
• Brings up a live WalletService (mainnet), imports the funded test wallet from env (never a source literal, never logged), calls balance_for_address(&addr, BalanceAsset::Xch), and asserts a real confirmed balance (result.balance > 0) — a Known reading, not Unknown — plus surfaces WalletBalanceResult { balance, pending, synced, peak_height } so the confirmed/pending/syncing shapes are exercised.

Verification

• cargo fmt --all -- --check → 0 · cargo clippy -p dig-node-service --all-targets --all-features -- -D warnings → 0 · cargo build --tests -p dig-node-service → 0 (the #[ignore]d test compiles) · cargo test -p dig-node-service --test live_funds_tip_e2e → 0 passed, 2 ignored (the live tests are skipped in CI).
• No secrets in source or commit — the mnemonic is read from DIG_TEST_WALLET_MNEMONIC at runtime only, never echoed or committed (/.test-credentials stays untouched and git-ignored).
• To run locally: DIG_LIVE_FUNDS_TEST=1 DIG_TEST_WALLET_MNEMONIC=… cargo test -p dig-node-service --test live_funds_tip_e2e -- --ignored.

Version

test: (test-only addition; the version-increment gate requires a bump) → [workspace.package].version 0.75.4 → 0.75.5. Cargo.lock updated + committed.

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