fix(cloud-agent-next): round session usage to two decimals

[kilo-code-bot]

Summary

Cloud Agent Token Usage on the web was shown to four decimal places (e.g. $1.2346). Round it to cents ($1.23) so session usage matches ordinary dollar display.

• formatSessionCost now uses two-decimal half-up rounding
• Component rows still reconcile to the displayed total
• Amounts below half a cent are hidden instead of rendering $0.00

Verification

• session-cost-breakdown.test.ts and ChatHeader.test.ts (96 tests) passed via Jest without the PostgreSQL worker setup
• No manual UI pass in this environment (no local Cloud Agent session)

Visual Changes

Token Usage in the chat header and session info dialog now shows $1.23 instead of $1.2346. Totals under $0.005 no longer appear.

Reviewer Notes

Per-message API request costs still use four decimals; only session Token Usage is two decimals.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Session Token Usage rounding was scaled from four decimals to cents with matching hide-below-half-cent thresholds; tests cover the new precision and I found no correctness issues.

Files Reviewed (3 files)

• apps/web/src/components/cloud-agent-next/session-cost-breakdown.ts
• apps/web/src/components/cloud-agent-next/session-cost-breakdown.test.ts
• apps/web/src/components/cloud-agent-next/ChatHeader.test.ts

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_{Reviewed by grok-4.6 · Input: 102.7K · Output: 10.8K · Cached: 132.9K}

_{Review guidance: REVIEW.md from base branch main}