feat(admin): add compute charge observability

[pandemicsyn]

Summary

• Add paid/shadow mode, accepted rate, settled seconds, settled amount, and Cloud Agent session links to Cloud Billing usage records.
• Add a read-only charge ledger with bounded payer, interval, session, SKU, and date filters plus cursor pagination.
• Add exact Cloud Agent session lookup and bookmarkable interval/session deep links for support investigations.

Stacked on #5358. This PR contains only the admin observability commit and should merge after its base PR.

Verification

• Browser-tested the populated Charges tab against local PostgreSQL using a fake admin account.
• Verified real payer, interval, and session-trace links.
• Verified an interval deep link restored Usage Records and showed Paid · 14s settled with the exact settled amount.
• Verified a session deep link restored session search and returned both related sandbox intervals.
• Verified conflicting user and organization filters produce an accessible inline validation error.
• Checked desktop and 375px mobile layouts; the dense ledger table scrolls horizontally on narrow screens.

Visual Changes

New charges tab in cloud billing admin ui:

Reviewer Notes

• Charge amounts come directly from immutable compute_usage_charge rows. Interval settled totals use decimal-string arithmetic matching the meter's cumulative flooring semantics.
• Searches require a maximum 31-day window. Payer filters use existing payer/time indexes; interval and session support queries remain bounded and partition-prunable without a schema migration.
• The ledger is intentionally read-only. This PR adds no refunds, corrections, interval mutations, rollout controls, schema changes, or customer-facing UI.
• Automated checks passed: 59 focused web tests, web typecheck/lint, root lint, formatting, and git diff --check. Independent static review found no blocking defects.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 files)

• apps/web/src/app/admin/cloud-billing-skus/UsageRecordsContent.tsx

Previous Review Summary (commit 36c7357)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit 36c7357)

Status: 1 Issue Found | Recommendation: Address before merge

Executive Summary

Session deep links query a 7-day window while the visible From/To fields still default to 24 hours, so the next Search changes the result set.

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	0

Issue Details (click to expand)

WARNING

File	Line	Issue
apps/web/src/app/admin/cloud-billing-skus/UsageRecordsContent.tsx	313	Session deep-link query window does not match the displayed date inputs

Files Reviewed (7 files)

• apps/web/src/app/admin/cloud-billing-skus/ChargesContent.tsx - 0 issues
• apps/web/src/app/admin/cloud-billing-skus/UsageRecordsContent.tsx - 1 issue
• apps/web/src/app/admin/cloud-billing-skus/page.tsx - 0 issues
• apps/web/src/lib/cloud-billing-sku.ts - 0 issues
• apps/web/src/lib/cloud-billing-sku.test.ts - 0 issues
• apps/web/src/routers/admin/cloud-billing-skus-router.ts - 0 issues
• apps/web/src/routers/admin/cloud-billing-skus-router.test.ts - 0 issues

Fix these issues in Kilo Cloud

---

_{Reviewed by grok-4.6 · Input: 63.4K · Output: 6.1K · Cached: 218.5K}

_{Review guidance: REVIEW.md from base branch feat/cloud-agent-paid-container-billing}