📦 添加虚拟环境和启动脚本

新增:
- backend/venv/ - Python 虚拟环境
- backend/start.sh - 启动脚本（使用虚拟环境）
- backend/requirements.txt - 依赖列表
- .gitignore - 忽略虚拟环境和缓存文件

说明:
- 每个项目使用独立虚拟环境
- 避免依赖冲突
- 启动脚本自动创建和激活虚拟环境

frontend/node_modules/@jridgewell/sourcemap-codec/src/strings.ts

@@ -0,0 +1,65 @@
+const bufLength = 1024 * 16;
+
+// Provide a fallback for older environments.
+const td =
+  typeof TextDecoder !== 'undefined'
+    ? /* #__PURE__ */ new TextDecoder()
+    : typeof Buffer !== 'undefined'
+      ? {
+          decode(buf: Uint8Array): string {
+            const out = Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength);
+            return out.toString();
+          },
+        }
+      : {
+          decode(buf: Uint8Array): string {
+            let out = '';
+            for (let i = 0; i < buf.length; i++) {
+              out += String.fromCharCode(buf[i]);
+            }
+            return out;
+          },
+        };
+
+export class StringWriter {
+  pos = 0;
+  private out = '';
+  private buffer = new Uint8Array(bufLength);
+
+  write(v: number): void {
+    const { buffer } = this;
+    buffer[this.pos++] = v;
+    if (this.pos === bufLength) {
+      this.out += td.decode(buffer);
+      this.pos = 0;
+    }
+  }
+
+  flush(): string {
+    const { buffer, out, pos } = this;
+    return pos > 0 ? out + td.decode(buffer.subarray(0, pos)) : out;
+  }
+}
+
+export class StringReader {
+  pos = 0;
+  declare private buffer: string;
+
+  constructor(buffer: string) {
+    this.buffer = buffer;
+  }
+
+  next(): number {
+    return this.buffer.charCodeAt(this.pos++);
+  }
+
+  peek(): number {
+    return this.buffer.charCodeAt(this.pos);
+  }
+
+  indexOf(char: string): number {
+    const { buffer, pos } = this;
+    const idx = buffer.indexOf(char, pos);
+    return idx === -1 ? buffer.length : idx;
+  }
+}