Improper formatting of `$0.0000` values

[MarcinOrlowski]

Improper formatting of $0.0000 values - seems like one digit too much for this one:

[iamtoruk]

Fixed — the formatCost() function in src/currency.ts was using toFixed(4) for all costs below $0.01, which produced $0.0000 for near-zero/zero values.

The fix keeps 4-decimal precision for real sub-cent costs (≥ $0.0001) but falls back to $0.00 for anything smaller. Will be in the next release.