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/20260331100001_create_users.up.sql

@@ -0,0 +1,13 @@
+CREATE TABLE users (
+    id            BIGSERIAL PRIMARY KEY,
+    email         VARCHAR(255) NOT NULL,
+    phone         VARCHAR(20),
+    password_hash VARCHAR(255) NOT NULL,
+    name          VARCHAR(100) NOT NULL,
+    avatar_url    TEXT,
+    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 UNIQUE INDEX uk_users_email_active ON users(email) WHERE deleted_at IS NULL;