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/20260331100006_create_tenant_quota_ledgers.up.sql

@@ -0,0 +1,12 @@
+CREATE TABLE tenant_quota_ledgers (
+    id             BIGSERIAL PRIMARY KEY,
+    tenant_id      BIGINT NOT NULL REFERENCES tenants(id),
+    quota_type     VARCHAR(50) NOT NULL,
+    delta          INT NOT NULL,
+    balance_after  INT NOT NULL,
+    reason         VARCHAR(255),
+    reference_type VARCHAR(50),
+    reference_id   BIGINT,
+    created_at     TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_tenant_quota_tenant_type_created ON tenant_quota_ledgers(tenant_id, quota_type, created_at DESC);