fix: use float division for COCOMO monthly wage so non-divisible avg-wage is not truncated

[YuriNachos]

Summary

• EstimateCost computed the monthly wage as float64(averageWage/12) — the division averageWage/12 is Go integer division (both operands int64), truncated to a whole number BEFORE the float64(...) cast runs. Any annual wage not evenly divisible by 12 was therefore silently under-counted. The shipped default --avg-wage 56286 has a monthly wage of 4690.5, but was truncated to 4690.
• Fix: move the cast in front of the division → float64(averageWage) / 12. One-line change.

Root cause

// before — integer divide inside the cast:
return effortApplied * float64(averageWage/12) * overhead
// after  — cast before divide, so the division is float:
return effortApplied * float64(averageWage) / 12 * overhead

Changes

File	Change
processor/cocomo.go	float64(averageWage/12) → float64(averageWage) / 12.
processor/cocomo_test.go	TestEstimateCostManyLines expected window updated from the truncated value (~2602096) to the correct one (~2602469) — the old assertion had hardcoded the buggy output. New TestEstimateCostMonthlyWagePrecision asserts the non-truncated monthly wage for the default 56286 (4690.5), red on master's truncated code and green after the fix.

Different file and different concern from the open F# PR #737 (languages.json); no conflict with any open PR.

Validation

• go test ./processor/ -run TestEstimateCost — TestEstimateCostManyLines + TestEstimateCostMonthlyWagePrecision both pass.
• Red-before-green: on master the new precision test fails (truncated 4690 vs 4690.5); after the one-line fix it passes. Reverting the fix re-fails it.
• go generate — no diff (cocomo.go is not a generate-input).

I licence this contribution under the MIT licence.