Add AI chat with skills management and model provider settings

- Model providers for OpenAI and Anthropic message formats (e.g. via
  Sub2API), with API keys encrypted at rest and never returned
- Skills tree with markdown editing, priorities, drafts, publishing and
  rollback; only published skills enter the chat prompt
- Chat page with tool calls over collected news and Binance USD-M
  klines, a persisted CONTEXT.md, reset, and stop-generation support
- Chat may only create skill drafts and update CONTEXT.md; publishing,
  deleting, moving and priority changes stay with the user

web/src/styles/index.css

@@ -8,3 +8,70 @@ body,
 body {
   font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
 }
+
+/* Markdown 渲染（Chat 回复、skill 预览、CONTEXT.md 预览） */
+.markdown-body {
+  font-size: 14px;
+  line-height: 1.7;
+  word-break: break-word;
+}
+.markdown-body > :first-child {
+  margin-top: 0;
+}
+.markdown-body h1,
+.markdown-body h2,
+.markdown-body h3,
+.markdown-body h4 {
+  margin: 1em 0 0.5em;
+  font-weight: 600;
+}
+.markdown-body h1 {
+  font-size: 1.5em;
+}
+.markdown-body h2 {
+  font-size: 1.3em;
+}
+.markdown-body h3 {
+  font-size: 1.1em;
+}
+.markdown-body p,
+.markdown-body ul,
+.markdown-body ol,
+.markdown-body pre,
+.markdown-body table,
+.markdown-body blockquote {
+  margin: 0.5em 0;
+}
+.markdown-body ul,
+.markdown-body ol {
+  padding-left: 1.5em;
+}
+.markdown-body code {
+  padding: 0.1em 0.3em;
+  border-radius: 3px;
+  background: var(--el-fill-color);
+  font-size: 0.9em;
+}
+.markdown-body pre {
+  padding: 0.6em 0.8em;
+  overflow: auto;
+  border-radius: 4px;
+  background: var(--el-fill-color-light);
+}
+.markdown-body pre code {
+  padding: 0;
+  background: none;
+}
+.markdown-body blockquote {
+  padding-left: 0.8em;
+  border-left: 3px solid var(--el-border-color);
+  color: var(--el-text-color-secondary);
+}
+.markdown-body table {
+  border-collapse: collapse;
+}
+.markdown-body th,
+.markdown-body td {
+  padding: 0.3em 0.6em;
+  border: 1px solid var(--el-border-color);
+}