fix(billing): show the cent Orb rounds up on per-metric charges

[macko911]

Context

orbAmountToCents reads money off Orb's decimal strings by taking the first two digits after the point. Invoice fields arrive already rounded to two decimals, so that was fine there.

The costs endpoint is not. It answers in full float precision, where two cents arrives as 0.01999999999999999872 — and dropping the extra digits makes that one cent. That endpoint feeds the per-metric Charges column on the billing page, which every customer has seen since #7364. So affected accounts are shown a cent less than Orb bills them.

Changes

• Round half-up on the third decimal instead of truncating, still reading digits off the string rather than via Number(x) * 100.
• Carry the rounding into the whole part, so 0.999 is a dollar rather than 99 cents.

Testing

Covers the real Orb value that exposed this (0.01999999999999999872 → 2 cents), the half-up boundary either side (19.994 / 19.995), and the carries 0.999 and 1.999.

Checked against live Orb for all ten pay-as-you-go accounts. Six showed a connections charge a cent below the matching invoice line; all ten agree after the fix. To see it on the billing page, open Usage for an account whose usage lands near a cent boundary and compare the Charges column against the Orb invoice.

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}