feat: 前端迁移至 TypeScript，集成 Biome 格式化与代码检查

- app.js → app.ts：添加完整类型标注、接口定义
- audio-processor.js → audio-processor.ts：AudioWorklet 类型化
- vite.config.js → vite.config.ts
- 添加 tsconfig.json、vite-env.d.ts
- 集成 Biome 默认配置（lint + format），通过全部检查
- package.json 添加 check/typecheck 脚本
- index.html 修复无障碍问题（button type、SVG title）

web/audio-processor.ts

@@ -0,0 +1,88 @@
+/**
+ * AudioWorklet processor for VoicePaste.
+ *
+ * Captures raw Float32 PCM from the microphone, accumulates samples into
+ * ~200ms frames, and posts them to the main thread for resampling + WS send.
+ *
+ * Communication:
+ *   Main → Processor: { command: "start" | "stop" }
+ *   Processor → Main: { type: "audio", samples: Float32Array, sampleRate: number }
+ */
+
+// AudioWorkletGlobalScope globals (not in standard lib)
+declare const sampleRate: number;
+declare class AudioWorkletProcessor {
+	readonly port: MessagePort;
+	constructor();
+	process(
+		inputs: Float32Array[][],
+		outputs: Float32Array[][],
+		parameters: Record<string, Float32Array>,
+	): boolean;
+}
+declare function registerProcessor(
+	name: string,
+	ctor: new () => AudioWorkletProcessor,
+): void;
+
+class VoicePasteProcessor extends AudioWorkletProcessor {
+	private recording = false;
+	private buffer: Float32Array[] = [];
+	private bufferLen = 0;
+	private readonly frameSize: number;
+
+	constructor() {
+		super();
+		// ~200ms worth of samples at current sample rate
+		this.frameSize = Math.floor(sampleRate * 0.2);
+
+		this.port.onmessage = (e: MessageEvent) => {
+			if (e.data.command === "start") {
+				this.recording = true;
+				this.buffer = [];
+				this.bufferLen = 0;
+			} else if (e.data.command === "stop") {
+				if (this.bufferLen > 0) {
+					this.flush();
+				}
+				this.recording = false;
+			}
+		};
+	}
+
+	process(inputs: Float32Array[][]): boolean {
+		if (!this.recording) return true;
+
+		const input = inputs[0];
+		if (!input || !input[0]) return true;
+
+		const channelData = input[0];
+		this.buffer.push(new Float32Array(channelData));
+		this.bufferLen += channelData.length;
+
+		if (this.bufferLen >= this.frameSize) {
+			this.flush();
+		}
+
+		return true;
+	}
+
+	private flush(): void {
+		const merged = new Float32Array(this.bufferLen);
+		let offset = 0;
+		for (const chunk of this.buffer) {
+			merged.set(chunk, offset);
+			offset += chunk.length;
+		}
+
+		this.port.postMessage(
+			{ type: "audio", samples: merged, sampleRate: sampleRate },
+			[merged.buffer],
+		);
+
+		this.buffer = [];
+		this.bufferLen = 0;
+	}
+}
+
+registerProcessor("audio-processor", VoicePasteProcessor);