[18India] Fix connection bonus fires on visited but unpaid cities

[ddaybell]

Summary

• connection_bonus was using route.visited_stops instead of the stops (paid stops) argument
• This caused the R+ route bonus to fire when both endpoint cities of a bonus pair were merely visited rather than counted among the train's paid cities
• A 4E train visiting Karachi and Chennai but paying for 4 other cities would incorrectly collect the R+80 bonus; now both cities must be among the paid stops

Fixes #11512

This will very likely require pinning games, as it changes the amounts awarded for many E train runs.

Test plan

• 18India fixtures: 43/43 pass
• Manual: run a 4E train that visits but does not pay for both cities of a bonus pair; confirm R+ does not appear
• Manual: run a 4E that pays for both cities of a bonus pair; confirm R+ still appears

[perwestling]

PR Review: #12712 - [18India] Fix connection bonus fires on visited but unpaid cities

Reviewed with AI assistance by Mistral Vibe

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✅ Strengths

• Fixes documented bug (#11512)
• Minimal, surgical change (2 lines)
• Correct root cause: was using route.visited_stops instead of paid stops
• All 18India fixtures pass (43/43)

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💡 Strong Recommendation

Since 18India has existing fixtures, please add a test case for this fix. State-based fixture preferred, but a unit test for the connection_bonus method is also acceptable.

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✅ Verdict: Approve

The fix is correct. 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 case that:

1. Runs a 4E train that visits but does not pay for both cities of a bonus pair
2. Confirms R+ does not appear
3. Runs a 4E that pays for both cities
4. Confirms R+ appears

Alternative: If setting up the game state is complex, a unit test for connection_bonus method verifying it uses the stops parameter (not route.visited_stops) would also work.

Remove AI assisted approval.