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

templates/pages/repo.html

@@ -177,7 +177,7 @@
         async function init() {
             try {
                 // Load repo info
-                const reposResp = await fetch('/api/repos');
+                const reposResp = await fetch('/api/repos', { credentials: 'same-origin' });
                 if (reposResp.ok) {
                     const repos = await reposResp.json();
                     const repo = repos.find(r => r.id == repoId || r.id === parseInt(repoId));
@@ -192,14 +192,14 @@
                 }
 
                 // Load refs
-                const refsResp = await fetch(`/api/repos/${repoId}/refs`);
+                const refsResp = await fetch(`/api/repos/${repoId}/refs`, { credentials: 'same-origin' });
                 if (refsResp.ok) {
                     currentRefs = await refsResp.json();
 
                     // Fetch recent commits independently
                     let commits = [];
                     try {
-                        const graphResp = await fetch(`/api/repos/${repoId}/graph?max_commits=20`);
+                        const graphResp = await fetch(`/api/repos/${repoId}/graph?max_commits=20`, { credentials: 'same-origin' });
                         if (graphResp.ok) { const gd = await graphResp.json(); commits = gd.commits || []; }
                     } catch (e) { /* ignore */ }