feat: 添加用户注册登录功能，实现数据和配置的用户隔离

- 新增 users 和 user_settings 表，repositories/analyses/review_notes 添加 user_id 列
- 实现基于邮箱+密码的注册登录，密码使用 bcrypt 哈希
- 使用 gin-contrib/sessions cookie-based session 管理
- 所有仓库、分析记录、review notes 按用户隔离
- 用户设置（LLM 配置、review 参数、缓存配置）独立存储
- 新增登录/注册页面，导航栏显示用户邮箱和退出按钮
- 前端 fetch 请求统一添加 credentials: 'same-origin'
- 支持 SESSION_SECRET 环境变量配置会话密钥

static/js/diff-viewer.js

@@ -668,7 +668,7 @@ const DiffViewer = {
 
         try {
             const url = `/api/repos/${repoId}/diff?base=${encodeURIComponent(base)}&head=${encodeURIComponent(head)}`;
-            const resp = await fetch(url);
+            const resp = await fetch(url, { credentials: 'same-origin' });
             if (!resp.ok) throw new Error('Failed to load diff');
 
             const data = await resp.json();
@@ -690,7 +690,7 @@ const DiffViewer = {
 
         try {
             const url = `/api/repos/${repoId}/diff?base=${encodeURIComponent(base)}&head=${encodeURIComponent(head)}&per_file=true`;
-            const resp = await fetch(url);
+            const resp = await fetch(url, { credentials: 'same-origin' });
             if (!resp.ok) throw new Error('Failed to load diff');
 
             const files = await resp.json();