feat(Phase-6): Admin, audit API, and reconciliation

[chitrank2050]

Overview

This is the tracking issue for Phase 6. The goal is to make Meterplex operable — admin dashboard APIs, queryable audit logs, dead letter replay, reconciliation jobs, and the credit/wallet system deferred from earlier phases.

Phases 1-5 build the billing engine. Phase 6 makes it manageable by humans.

Success Criteria

• Admin can query audit logs with filters (actor, resource, tenant, date range)
• Admin can view, retry, and discard dead letter events via API
• Reconciliation job compares raw usage vs billed usage and flags mismatches
• Reconciliation job compares subscription state vs payment state
• AI credits / wallet system with prepaid balance, top-ups, and discounts
• Daily limit support (DAILY reset period) for features
• Usage summary endpoint with percentage breakdowns (daily, monthly, annual)
• Timezone-aware billing period boundaries
• Invoice PDF generation for tenant download
• Export usage and invoice reports (CSV/JSON)
• All admin actions audit-logged

Tracking / Sub-tasks

• feat(admin): audit log query API with filters and pagination #154
• feat(admin): dead letter event management API #155
• feat(admin): reconciliation job — raw usage vs billed usage comparison #156
• feat(admin): reconciliation job — subscription state vs payment state comparison #157
• feat(credits): credit wallet schema and service for prepaid balance #158
• feat(credits): credit purchase with discount and promotional pricing #159
• feat(credits): deduct credits on usage consumption #160
• feat(entitlements): add DAILY reset period for features #161
• feat(usage): usage summary endpoint with percentage breakdowns #162
• feat(billing): timezone-aware billing period boundaries #163
• feat(invoices): PDF invoice generation for tenant download #164
• feat(admin): export usage and invoice reports (CSV/JSON) #165
• feat(seed): add credit wallet, reconciliation, and export sample data #166
• docs(phase-6): finalize documentation and Bruno collection #167

Resources

• Architecture Log: docs/phases/phase-6.md (to be created)
• Architecture Doc: docs/architecture/phase-6-admin-reconciliation.md (to be created)
• Security Audit: docs/audits/security-audit-v2.md

Why this phase matters

A billing system without admin tooling is a black box. When a tenant disputes a charge, the support team needs to query audit logs, inspect usage, compare against invoices, and identify discrepancies. When usage events fail, someone needs to investigate and replay them. When a tenant wants prepaid credits instead of postpaid billing, the system needs to support both models.

This phase transforms Meterplex from "it works" to "it's operable."

Note: This issue represents the "Phase 6" milestone. Individual PRs should reference the specific sub-tasks above.