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/20260331100013_create_generation_tasks.up.sql

@@ -0,0 +1,18 @@
+CREATE TABLE generation_tasks (
+    id                   BIGSERIAL PRIMARY KEY,
+    tenant_id            BIGINT NOT NULL REFERENCES tenants(id),
+    article_id           BIGINT REFERENCES articles(id),
+    task_batch_id        VARCHAR(100),
+    quota_reservation_id BIGINT REFERENCES quota_reservations(id),
+    task_type            VARCHAR(50) NOT NULL,
+    request_hash         VARCHAR(64),
+    input_params_json    JSONB,
+    status               VARCHAR(20) NOT NULL DEFAULT 'queued',
+    error_message        TEXT,
+    started_at           TIMESTAMPTZ,
+    completed_at         TIMESTAMPTZ,
+    created_at           TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at           TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_generation_task_status_created ON generation_tasks(status, created_at);
+CREATE INDEX idx_generation_task_tenant ON generation_tasks(tenant_id, created_at DESC);