[18India] Fix hand share purchase price to use IPO price

[ddaybell]

Summary

• can_buy_from_hand? and can_buy_company? affordability checks for hand share certificates now use IPO/par price explicitly via a new hand_price(company) helper, rather than company.value which can reflect market price when the underlying share's ownership changes
• hand_price computes par_price * num_shares for :share and :president type certificates; falls back to company.value for other types or if par_price is unavailable

Test plan

• All 185 existing fixture tests pass
• Verify a player can buy a hand share certificate at IPO price when the corporation's market price has moved above or below the original IPO price

Closes #11114

?? Generated with Claude Code

[perwestling]

PR Review: #12714 - [18India] Fix hand share purchase price to use IPO price

Reviewed with AI assistance by Mistral Vibe

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✅ Strengths

• Fixes documented issue (#11114)
• Minimal, focused change (13 lines added, 2 removed)
• Correct root cause: was using company.value (market price) instead of IPO/par price for hand certificates
• All 18India fixtures pass (43/43)
• Clean helper method (hand_price) with proper fallbacks

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💡 Strong Recommendation

Since 18India has existing fixtures, please add a test case verifying:

• Hand share certificates use IPO price, not market price
• Fallback to company.value for other certificate types
• Behavior is correct when market price differs from IPO price

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❓ Questions

• Have you verified the manual test case mentioned in the PR description?

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✅ Verdict: Approve

The fix is correct and addresses a real bug. Adding a test is strongly recommended but not blocking.

[perwestling]

Strongly recommend: Add state-based fixture test

Since 18India has existing fixtures, please add a test that verifies:

1. A player can buy a hand share certificate at IPO price when corporation's market price is above IPO price
2. A player can buy a hand share certificate at IPO price when corporation's market price is below IPO price
3. Non-share/president certificates still use company.value

This prevents regression of the price calculation logic.

Remove AI assisted approval.