Add coverage for Bank deposit/withdraw invalid-amount retry

[dmccoystephenson]

Summary

• Full triage found no open issues/PRs and no documentation drift (README, PLANNING.md, and all three schemas/*.json match their models). No backlog work was skipped/deferred this cycle since the backlog was empty.
• This cycle is a Stage B unit-test-expansion cycle: src/location/bank.py was the only source file with a coverage gap that represents a real, player-reachable behavior — Bank.deposit()/Bank.withdraw() each loop back and re-prompt when promptForNumber returns None (i.e. the player typed something non-numeric), but neither retry branch had a test.
• Added test_deposit_invalid_input_retries_then_succeeds and test_withdraw_invalid_input_retries_then_succeeds, mirroring the sibling test structure already in tests/location/test_bank.py, using side_effect=[None, 10.0] to exercise the retry-then-succeed path deterministically.
• src/location/bank.py is now at 100% line coverage (was 96%, missing exactly these two branches).

Test plan

• python3 -m compileall -q src
• Full suite (headless SDL): 404 passed, 0 failed
• tests/location/test_bank.py alone: 25 passed
• Coverage check confirms src/location/bank.py at 100%, no other file regressed

Closes: none — no tracking issue existed; this is a proactive Stage B test-expansion cycle per the dev-loop's tiebreaker (documentation/coverage work preferred when the issue backlog is empty).

[dmccoystephenson]

Self-review rubric:

• Scope: PASS — only tests/location/test_bank.py touched; both new tests target exactly the coverage gap (deposit/withdraw's promptForNumber is None retry branch) called out in the PR description.
• Tests-new: PASS — test_deposit_invalid_input_retries_then_succeeds and test_withdraw_invalid_input_retries_then_succeeds each exercise the retry-then-succeed path via side_effect=[None, 10.0] and assert call_count == 2 plus the final balances.
• Tests-fix: N/A — this is a Stage B test-expansion cycle, not a bug fix; no production code changed.
• Sibling structure: PASS — new tests reuse createBank(), the same MagicMock-ing of lotsOfSpace/divider, and the # prepare / # call / # check comment structure used by every neighboring test in the file.
• Sibling renames: N/A — no renames in this PR.
• Docs: PASS — no behavior changed (test-only PR), so README/PLANNING.md/schemas are unaffected; verified none needed updating.
• Issue resolution: N/A — no tracking issue existed (noted in the PR body); this was proactive coverage work found during triage.
• CI: PASS — test check green on the PR head (https://github.com/Stephenson-Software/FishE/actions/runs/30521784758).

Repo-specific:

• Schema-sync: N/A — no persisted fields touched.
• Money-format: N/A — no display strings touched.
• Deterministic-tests: PASS — side_effect=[None, 10.0] is a fixed sequence, no unseeded random involved.
• Headless-pygame: N/A — Bank/console-agnostic UI mock, no pygame surface touched.
• camelCase: PASS — new test function names (test_deposit_invalid_input_retries_then_succeeds, test_withdraw_invalid_input_retries_then_succeeds) follow the file's existing test_<behavior> snake_case pytest convention.

Coverage confirms src/location/bank.py moved from 96% (missing the two continue branches) to 100% with this PR, and the full suite (404 tests, headless SDL) still passes.