feat: 完善多模型配置与运行切换

将模型连接统一持久化管理，并支持 Agent 运行中切换模型以及中断后选择模型继续。补充配置校验、事务与前后端交互测试。

web-ui/src/styles.css

@@ -153,27 +153,37 @@ a { color: inherit; text-decoration: none; }
 .back-to-bottom { position: fixed; right: 32px; bottom: 28px; width: 38px; height: 38px; border: 0; border-radius: 50%; background: #fff; color: var(--blue); box-shadow: 0 6px 22px rgba(29, 58, 111, .14); cursor: pointer; }
 .back-to-bottom:focus-visible { outline: 2px solid var(--blue); outline-offset: 2px; }
 .empty-main { display: grid; place-items: center; min-height: 100vh; color: #8995a8; }
+.model-picker-field { display: grid; grid-template-columns: 86px minmax(0, 1fr); align-items: center; gap: 14px; min-height: 52px; }
+.model-picker-field > span { color: #53617b; font-size: 14px; }
 
 .settings-page { min-height: 100vh; padding: 28px 42px; }
 .settings-page > header h1 { margin: 0; font-size: 28px; }
 .settings-page > header p { color: #5f6d86; margin: 10px 0 0; }
+.settings-header { display: flex; align-items: flex-start; justify-content: space-between; gap: 24px; }
 .settings-grid { display: grid; grid-template-columns: 380px minmax(520px, 1fr); margin-top: 38px; min-height: 740px; }
 .settings-list { padding-right: 28px; border-right: 1px solid var(--line); }
 .settings-list h2, .skill-list h2 { font-size: 18px; margin: 0 0 18px; }
+.settings-list h2 small { margin-left: 6px; color: #7b879b; font-size: 13px; font-weight: 500; }
 .settings-list button { width: 100%; display: grid; grid-template-columns: 1fr auto; text-align: left; padding: 18px 16px; border: 0; border-radius: 7px; background: #fff; cursor: pointer; }
 .settings-list button.selected { background: #edf4ff; color: var(--blue); }
+.settings-list button.disabled strong, .settings-list button.disabled span { color: #8b96a8; }
 .settings-list button strong, .settings-list button span { grid-column: 1; }
 .settings-list button span { margin-top: 8px; color: #5f6d86; }
 .settings-list button small { grid-column: 2; grid-row: 1 / span 2; align-self: end; color: var(--green); }
+.settings-list button small.muted { color: #8b96a8; }
 .settings-list button i, .skill-list button > i { display: inline-block; width: 7px; height: 7px; border-radius: 50%; background: var(--green); margin-right: 6px; }
+.settings-list button small.muted i { background: #9ca6b5; }
+.model-empty { min-height: 160px; display: grid; place-items: center; color: #8995a8; border: 1px dashed #d9e0ea; border-radius: 7px; }
 .settings-form { padding-left: 28px; }
 .form-title { height: 62px; display: flex; align-items: start; justify-content: space-between; border-bottom: 1px solid var(--line); }
 .form-title h2 { margin: 0; font-size: 22px; }
+.model-title-actions { display: flex; align-items: center; gap: 10px; }
 .settings-form > label { display: grid; grid-template-columns: 170px minmax(320px, 1fr); align-items: center; min-height: 88px; border-bottom: 1px solid var(--line); }
 .capability-row { display: grid; grid-template-columns: 170px 1fr; min-height: 88px; align-items: center; border-bottom: 1px solid var(--line); }
 .capability-row div { display: flex; gap: 8px; }
 .capability-row b { padding: 6px 10px; border: 1px solid #d3dbe7; border-radius: 5px; font-size: 13px; font-weight: 500; }
 .model-actions { display: flex; align-items: center; gap: 16px; padding-top: 28px; }
+.model-danger-actions { display: flex; align-items: center; gap: 10px; margin-left: auto; }
 .connection-ok { color: var(--green); display: inline-flex; align-items: center; gap: 6px; }
 .connection-ok svg { width: 18px; }
 
@@ -229,6 +239,7 @@ a { color: inherit; text-decoration: none; }
   .work-scroll { width: calc(100% - 32px); }
   .page-header { padding: 0 16px; }
   .page-header h1 { max-width: 240px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; font-size: 20px; }
+  .run-actions { gap: 2px; }
   .ask-card, .artifact-card { max-width: 100%; margin-left: 0; }
   .flow-tool, .flow-reasoning, .flow-notice { padding-left: 28px; }
   .flow-tool::before, .flow-reasoning::before { left: 7px; }
@@ -236,10 +247,13 @@ a { color: inherit; text-decoration: none; }
   .material-item { grid-template-columns: 1fr 160px; }
   .material-upload { grid-column: 2; }
   .settings-page { padding: 24px 16px; }
+  .settings-header { align-items: center; }
   .settings-grid, .skill-grid { grid-template-columns: 1fr; }
   .settings-list, .skill-list { max-height: 300px; border-right: 0; border-bottom: 1px solid var(--line); padding: 0 0 20px; }
   .settings-form, .skill-detail { padding: 24px 0 0; }
   .settings-form > label, .capability-row { grid-template-columns: 130px 1fr; }
+  .model-actions { flex-wrap: wrap; }
+  .model-danger-actions { width: 100%; margin-left: 0; padding-top: 6px; }
 }
 
 @media (prefers-reduced-motion: reduce) {