chore: restore demo assets for local development

public/subtitles/intro_en.vtt

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+WEBVTT
+00:00.000 --> 00:02.000
+You wake up in a strange room
+00:02.500 --> 00:03.000
+Two doors stand before you. You must choose.

public/subtitles/investigation.vtt

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+WEBVTT
+
+00:00.000 --> 00:05.000
+你走进了一个凌乱的房间，仔细观察四周...

public/subtitles/left_door.vtt

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+WEBVTT
+
+00:00.000 --> 00:02.500
+你走进了发光的门，来到一个明亮的大厅
+
+00:02.500 --> 00:03.000
+一位陌生人向你伸出了手

public/subtitles/left_door_en.vtt

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+WEBVTT
+00:00.000 --> 00:02.500
+You enter the glowing door into a bright hall
+00:02.500 --> 00:03.000
+A stranger extends their hand toward you

public/subtitles/stay.vtt

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+WEBVTT
+
+00:00.000 --> 00:03.000
+你选择留在原地，时间缓缓流逝...

public/subtitles/stay_en.vtt

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+WEBVTT
+00:00.000 --> 00:03.000
+You choose to stay. Time passes slowly...