feat: add tenant and user management with migrations, handlers, and tests

- Implemented tenant and user management features including:
  - Tenant creation and management with associated migrations.
  - User creation and management with associated migrations.
  - Tenant membership management with associated migrations.
  - Platform user roles management with associated migrations.
  - Quota management with associated migrations.
  - Article and template management with associated migrations.
- Added HTTP handlers for templates and workspaces.
- Created tests for protected and public routes.
- Introduced a script to check tenant scope in SQL queries.
- Documented task plan for backend completion and frontend foundation.

server/internal/tenant/repository/queries/workspace.sql

@@ -0,0 +1,37 @@
+-- name: CountArticlesByTenant :one
+SELECT COUNT(*) FROM articles
+WHERE tenant_id = sqlc.arg(tenant_id) AND deleted_at IS NULL;
+
+-- name: CountPublishedArticlesByTenant :one
+SELECT COUNT(*) FROM articles
+WHERE tenant_id = sqlc.arg(tenant_id) AND publish_status = 'success' AND deleted_at IS NULL;
+
+-- name: CountBrandsByTenant :one
+SELECT COUNT(*) FROM brands
+WHERE tenant_id = sqlc.arg(tenant_id) AND deleted_at IS NULL;
+
+-- name: GetRecentArticles :many
+SELECT a.id, a.generate_status, a.publish_status, a.source_type, a.created_at,
+       av.title, av.word_count, av.source_label,
+       t.template_name
+FROM articles a
+LEFT JOIN article_versions av ON av.id = a.current_version_id
+LEFT JOIN article_templates t ON t.id = a.template_id
+WHERE a.tenant_id = sqlc.arg(tenant_id) AND a.deleted_at IS NULL
+ORDER BY a.created_at DESC
+LIMIT 10;
+
+-- name: GetQuotaSummary :one
+SELECT COALESCE(
+    (SELECT balance_after FROM tenant_quota_ledgers
+     WHERE tenant_id = sqlc.arg(tenant_id) AND quota_type = 'article_generation'
+     ORDER BY created_at DESC LIMIT 1), 0
+)::INT AS balance;
+
+-- name: GetActivePlanForTenant :one
+SELECT p.plan_code, p.name AS plan_name, p.quota_policy_json,
+       s.start_at, s.end_at
+FROM tenant_plan_subscriptions s
+JOIN plans p ON p.id = s.plan_id
+WHERE s.tenant_id = sqlc.arg(tenant_id) AND s.status = 'active' AND s.deleted_at IS NULL
+LIMIT 1;