重构代码结构并添加完整功能

主要改动：
- 重构目录结构：合并子目录到根目录，简化项目结构
- 添加完整的查询 API：支持复杂条件查询、字段选择、游标模式
- 实现 LSM-Tree Compaction：7层结构、Score-based策略、后台异步合并
- 添加 Web UI：基于 Lit 的现代化管理界面，支持数据浏览和 Manifest 查看
- 完善文档：添加 README.md 和 examples/webui/README.md

新增功能：
- Query Builder：链式查询 API，支持 Eq/Lt/Gt/In/Between/Contains 等操作符
- Web UI 组件：srdb-app、srdb-table-list、srdb-data-view、srdb-manifest-view 等
- 列选择持久化：自动保存到 localStorage
- 刷新按钮：一键刷新当前视图
- 主题切换：深色/浅色主题支持

代码优化：
- 使用 Go 1.24 新特性：range 7、min()、maps.Copy()、slices.Sort()
- 统一组件命名：所有 Web Components 使用 srdb-* 前缀
- CSS 优化：提取共享样式，减少重复代码
- 清理遗留代码：删除未使用的方法和样式

webui/static/js/components/modal-dialog.js

@@ -0,0 +1,179 @@
+import { LitElement, html, css } from 'https://cdn.jsdelivr.net/gh/lit/dist@3/core/lit-core.min.js';
+import { sharedStyles, cssVariables } from '../styles/shared-styles.js';
+
+export class ModalDialog extends LitElement {
+  static properties = {
+    open: { type: Boolean },
+    title: { type: String },
+    content: { type: String }
+  };
+
+  static styles = [
+    sharedStyles,
+    cssVariables,
+    css`
+    :host {
+      display: none;
+      position: fixed;
+      top: 0;
+      left: 0;
+      width: 100%;
+      height: 100%;
+      background: rgba(0, 0, 0, 0.7);
+      z-index: 1000;
+      align-items: center;
+      justify-content: center;
+    }
+
+    :host([open]) {
+      display: flex;
+    }
+
+    .modal-content {
+      background: var(--bg-surface);
+      border-radius: var(--radius-lg);
+      box-shadow: var(--shadow-xl);
+      min-width: 324px;
+      max-width: 90vw;
+      max-height: 80vh;
+      width: fit-content;
+      display: flex;
+      flex-direction: column;
+      border: 1px solid var(--border-color);
+    }
+
+    @media (max-width: 768px) {
+      .modal-content {
+        min-width: 300px;
+        max-width: 95vw;
+      }
+    }
+
+    .modal-header {
+      display: flex;
+      align-items: center;
+      justify-content: space-between;
+      padding: 20px 24px;
+      border-bottom: 1px solid var(--border-color);
+    }
+
+    .modal-header h3 {
+      margin: 0;
+      font-size: 18px;
+      font-weight: 600;
+      color: var(--text-primary);
+    }
+
+    .modal-close {
+      background: transparent;
+      border: none;
+      color: var(--text-secondary);
+      cursor: pointer;
+      padding: 4px;
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      border-radius: var(--radius-sm);
+      transition: var(--transition);
+    }
+
+    .modal-close:hover {
+      background: var(--bg-hover);
+      color: var(--text-primary);
+    }
+
+    .modal-body {
+      padding: 24px;
+      overflow-y: auto;
+      flex: 1;
+    }
+
+    pre {
+      /*background: var(--bg-elevated);*/
+      padding: 16px;
+      border-radius: var(--radius-md);
+      overflow-x: auto;
+      color: var(--text-primary);
+      font-family: 'Courier New', monospace;
+      font-size: 13px;
+      line-height: 1.5;
+      margin: 0;
+      white-space: pre-wrap;
+      word-wrap: break-word;
+    }
+  `
+  ];
+
+  constructor() {
+    super();
+    this.open = false;
+    this.title = 'Content';
+    this.content = '';
+    this._handleKeyDown = this._handleKeyDown.bind(this);
+  }
+
+  connectedCallback() {
+    super.connectedCallback();
+    document.addEventListener('keydown', this._handleKeyDown);
+  }
+
+  disconnectedCallback() {
+    super.disconnectedCallback();
+    document.removeEventListener('keydown', this._handleKeyDown);
+  }
+
+  updated(changedProperties) {
+    if (changedProperties.has('open')) {
+      if (this.open) {
+        this.setAttribute('open', '');
+      } else {
+        this.removeAttribute('open');
+      }
+    }
+  }
+
+  _handleKeyDown(e) {
+    if (this.open && e.key === 'Escape') {
+      this.close();
+    }
+  }
+
+  close() {
+    this.open = false;
+    this.dispatchEvent(new CustomEvent('modal-close', {
+      bubbles: true,
+      composed: true
+    }));
+  }
+
+  render() {
+    return html`
+      <div class="modal-content" @click=${(e) => e.stopPropagation()}>
+        <div class="modal-header">
+          <h3>${this.title}</h3>
+          <button class="modal-close" @click=${this.close}>
+            <svg
+              xmlns="http://www.w3.org/2000/svg"
+              width="20"
+              height="20"
+              viewBox="0 0 24 24"
+              fill="none"
+              stroke="currentColor"
+              stroke-width="2"
+              stroke-linecap="round"
+              stroke-linejoin="round"
+            >
+              <line x1="18" y1="6" x2="6" y2="18"></line>
+              <line x1="6" y1="6" x2="18" y2="18"></line>
+            </svg>
+          </button>
+        </div>
+        <div class="modal-body">
+          <pre>${this.content}</pre>
+        </div>
+      </div>
+    `;
+  }
+}
+
+customElements.define('srdb-modal-dialog', ModalDialog);