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/migrations/20260331100007_create_quota_reservations.up.sql

@@ -0,0 +1,15 @@
+CREATE TABLE quota_reservations (
+    id              BIGSERIAL PRIMARY KEY,
+    tenant_id       BIGINT NOT NULL REFERENCES tenants(id),
+    quota_type      VARCHAR(50) NOT NULL,
+    resource_type   VARCHAR(50) NOT NULL,
+    resource_id     BIGINT NOT NULL,
+    reserved_amount INT NOT NULL,
+    consumed_amount INT NOT NULL DEFAULT 0,
+    refunded_amount INT NOT NULL DEFAULT 0,
+    status          VARCHAR(20) NOT NULL DEFAULT 'pending',
+    expire_at       TIMESTAMPTZ NOT NULL,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_quota_reservation_tenant_status ON quota_reservations(tenant_id, status);