chore(openspec): archive phase-4-developer-growth change

All 90 tasks complete. Phase 4 — Developer Growth & Go-to-Market
fully delivered and archived per OpenSpec protocol.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

openspec/changes/archive/2026-04-02-phase-4-developer-growth/specs/web-dashboard/spec.md

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+## ADDED Requirements
+
+### Requirement: Usage dashboard tab displays per-tenant metering data
+The web dashboard SHALL include a "Usage" tab in the main navigation displaying the current billing period's usage: API calls used / daily limit, active agents count / agent limit, token issuances this period. Usage data SHALL be fetched from `GET /billing/usage` (new authenticated endpoint). The tab SHALL update on page load and on a 60-second polling interval.
+
+#### Scenario: Usage tab shows current metrics
+- **WHEN** an authenticated user navigates to the Usage tab
+- **THEN** the dashboard displays current API call count, agent count, and token issuance count for the current billing period
+
+#### Scenario: Free tier warning shown when approaching limit
+- **WHEN** a free-tier tenant has used ≥ 80% of their daily API call limit
+- **THEN** a warning banner is displayed with a link to the upgrade/pricing page
+
+### Requirement: Billing status panel shows subscription tier and upgrade CTA
+The web dashboard Usage tab SHALL include a billing status panel showing: current tier (Free / Paid), subscription status (active / cancelled / trial), and — for free-tier tenants — an "Upgrade" button linking to `POST /billing/checkout` flow.
+
+#### Scenario: Free tier tenant sees upgrade CTA
+- **WHEN** a free-tier tenant views the Usage tab
+- **THEN** an "Upgrade to Paid" button is visible and initiates Stripe Checkout when clicked
+
+#### Scenario: Paid tier tenant sees subscription status
+- **WHEN** a paid-tier tenant views the Usage tab
+- **THEN** the panel shows "Paid" tier with subscription status and next renewal date, with no upgrade CTA