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/20260331100022_create_brand_questions.up.sql

@@ -0,0 +1,12 @@
+CREATE TABLE brand_questions (
+    id                 BIGSERIAL PRIMARY KEY,
+    tenant_id          BIGINT NOT NULL REFERENCES tenants(id),
+    brand_id           BIGINT NOT NULL REFERENCES brands(id),
+    keyword_id         BIGINT NOT NULL REFERENCES brand_keywords(id),
+    current_version_id BIGINT,
+    status             VARCHAR(20) NOT NULL DEFAULT 'active',
+    created_at         TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at         TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    deleted_at         TIMESTAMPTZ
+);
+CREATE INDEX idx_brand_questions_keyword ON brand_questions(keyword_id);