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/20260331100031_create_audit_logs.up.sql

@@ -0,0 +1,12 @@
+CREATE TABLE audit_logs (
+    id          BIGSERIAL PRIMARY KEY,
+    operator_id BIGINT NOT NULL REFERENCES users(id),
+    tenant_id   BIGINT,
+    module      VARCHAR(50) NOT NULL,
+    action      VARCHAR(50) NOT NULL,
+    before_json JSONB,
+    after_json  JSONB,
+    result      VARCHAR(20),
+    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_audit_module_created ON audit_logs(module, created_at DESC);