Fix tavern money prompts truncating cents

[dmccoystephenson]

Summary

• player.money can hold a fractional value after a bank withdrawal (bank.py already parses withdraw/deposit amounts with float(input())), but three "Change Bet" prompts in tavern.py formatted self.player.money with %d, silently dropping the cents.
• Switched those three prompts (in gamble()'s "Change Bet" branch and changeBet()'s two outcome branches) to %.2f, matching the convention bank.py already uses for the same field.
• currentBet/winAmount/diceThrow displays were left as %d — those are always whole dollars by design (changeBet does self.amount = int(amount)), so no change needed there.

Test plan

• Added test_changeBet_invalid_input_shows_cents, test_changeBet_insufficient_money_shows_cents, and test_gamble_change_bet_prompt_shows_cents to tests/location/test_tavern.py, each asserting the generated prompt text retains cents (e.g. $42.70).
• Verified regression coverage: stashed the tavern.py fix, confirmed all three new tests fail against the old %d code, then restored the fix and confirmed they pass.
• python3 -m compileall -q src tests
• Full suite: 374 passed (SDL_VIDEODRIVER=dummy SDL_AUDIODRIVER=dummy python3 -m pytest)

Triage notes

• The repo's only open issue (PLANNING.md's only GOALS entry (bait price loading bug) may be stale #122, PLANNING.md's stale-looking bait-price GOALS entry) explicitly requires the repo owner's memory of the original bug symptom to resolve safely — left open, not picked for this cycle.

[dmccoystephenson]

Self-review rubric:

• Scope: PASS — only src/location/tavern.py (the three %d -> %.2f fixes) and its test file are touched; no unrelated formatting/renames.
• Tests-new: PASS — each new test exercises a real generation path (gamble()'s change-bet branch, changeBet()'s two outcome branches), not a hand-crafted literal string.
• Tests-fix: PASS — stashed src/location/tavern.py, ran the 3 new tests, confirmed all 3 FAIL ($42 instead of $42.70, etc.), popped the stash, confirmed all 3 PASS.
• Sibling structure: N/A — no new files.
• Sibling renames: N/A — no renamed identifiers.
• Docs: PASS — this is a display-format fix only, no persisted field/README/schema/PLANNING content changed.
• Issue resolution: N/A — no tracked issue closed by this PR (see triage note below).
• CI: PASS — test check green on the PR head (https://github.com/Stephenson-Software/FishE/actions/runs/30227748780).
• Schema-sync: N/A — no persisted field touched.
• Money-format: PASS — this PR's whole purpose is fixing a money value (player.money) displayed with %d; now %.2f, matching bank.py's existing convention for the same field. Verified the two %d fields left alone (currentBet, winAmount, diceThrow) are always ints by construction (changeBet does self.amount = int(amount)).
• Deterministic-tests: PASS — no new test touches random.
• Headless-pygame: N/A — no pygame code path touched.
• camelCase: PASS — no new identifiers introduced.

Triage note: the repo's only open issue (#122) is a stale-looking PLANNING.md GOALS entry that both the issue body and a follow-up comment concluded is not currently reproducible in code — but deliberately left open because only the repo owner can say whether the original symptom is something the code checks wouldn't catch. Not picked for this cycle; this PR fixes an independent bug found during the triage sweep instead (no tracking issue existed for it).