refactor: redesign planos interface with design system patterns

- Create CreatePlanModal component with Headless UI Dialog
- Implement dark mode support throughout plans UI
- Update plans/page.tsx with professional card layout
- Update plans/[id]/page.tsx with consistent styling
- Add proper spacing, typography, and color consistency
- Implement smooth animations and transitions
- Add success/error message feedback
- Improve form UX with better input styling

postgres/migrations/010_create_agency_subscriptions_table.sql

@@ -0,0 +1,24 @@
+-- Create agency_subscriptions table
+CREATE TABLE IF NOT EXISTS agency_subscriptions (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    agency_id UUID NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+    plan_id UUID NOT NULL REFERENCES plans(id) ON DELETE RESTRICT,
+    billing_type VARCHAR(20) NOT NULL DEFAULT 'monthly', -- monthly or annual
+    current_users INTEGER NOT NULL DEFAULT 0,
+    status VARCHAR(50) NOT NULL DEFAULT 'active', -- active, suspended, cancelled
+    start_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    renewal_date TIMESTAMP NOT NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    UNIQUE(agency_id) -- One active subscription per agency
+);
+
+-- Add indexes
+CREATE INDEX idx_agency_subscriptions_agency_id ON agency_subscriptions(agency_id);
+CREATE INDEX idx_agency_subscriptions_plan_id ON agency_subscriptions(plan_id);
+CREATE INDEX idx_agency_subscriptions_status ON agency_subscriptions(status);
+
+-- Add comments
+COMMENT ON TABLE agency_subscriptions IS 'Tracks agency subscription to plans';
+COMMENT ON COLUMN agency_subscriptions.billing_type IS 'Monthly or annual billing';
+COMMENT ON COLUMN agency_subscriptions.current_users IS 'Current count of users (collaborators + clients)';