Fix activity route distance rounding parity

[bhelm]

Summary

• make Kotlin degree-to-radian conversion use the same multiply-then-divide operation order as Swift
• preserve the earth radius, haversine expression, point order, and route accumulation order
• add mirrored exact-bit tests for the reachable three-point route and an adjacent one-segment control

Root cause

Swift computes radians as x * pi / 180, while Kotlin used Math.toRadians, whose different intermediate rounding changes the second segment and final three-point distance by one binary64 ULP. Kotlin now spells out Swift's operation order; Swift production is unchanged.

Validation

• RED before fix: the three-point Kotlin result was 0x403e89813f76c75d, while Swift and the independent oracle produced 0x403e89813f76c75c
• frozen three-file diff is an exact semantic subset of the independently reviewed product-fix union
• Swift exact focused tests: 2 passed
• Swift affected StrandImport suite: 28 tests passed
• Swift full StrandImport suite: 241 tests passed, 0 failures, 1 environment-dependent skip
• Kotlin exact focused tests: 2 passed
• Kotlin affected importer suite: 35 tests passed across the union's affected classes
• Kotlin FullDebug: 4,157 tests passed, 0 failures/errors, 6 skipped
• git diff --check: pass
• independent static review: pass, no P0/P1/P2

Fixes bhelm#99.