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/20260331100011_create_articles.up.sql

@@ -0,0 +1,15 @@
+CREATE TABLE articles (
+    id                 BIGSERIAL PRIMARY KEY,
+    tenant_id          BIGINT NOT NULL REFERENCES tenants(id),
+    source_type        VARCHAR(30) NOT NULL,
+    template_id        BIGINT REFERENCES article_templates(id),
+    prompt_rule_id     BIGINT,
+    current_version_id BIGINT,
+    generate_status    VARCHAR(20) NOT NULL DEFAULT 'pending',
+    publish_status     VARCHAR(20) NOT NULL DEFAULT 'unpublished',
+    created_at         TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at         TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    deleted_at         TIMESTAMPTZ
+);
+CREATE INDEX idx_article_tenant_created ON articles(tenant_id, created_at DESC);
+CREATE INDEX idx_article_tenant_status ON articles(tenant_id, generate_status, publish_status, created_at DESC);