Add demo dataset with placeholder video files

[Copilot]

Adds a ready-to-use demo/ directory of zero-byte placeholder files covering the full range of naming conventions, file extensions, and directory structures the scanner handles.

demo/source/ contents

Movies — one per supported separator style and extension:

File	Convention	Ext
Gullivers.Travels.1939.mkv	dot-separated	.mkv
The_Little_Shop_of_Horrors_1960.avi	underscore	.avi
Night of the Living Dead (1968).mp4	spaces + parens	.mp4
The-Stranger-1946.m4v	dash-separated	.m4v
White Zombie (1932)/White.Zombie.1932.mkv	dot, in subdirectory	.mkv

All movies are public domain (expired copyright).

TV Series — The Lone Ranger, Season 1, Episodes 1–3 in The Lone Ranger/ subdirectory, using S##E## dot-separated naming across .mkv, .avi, and .mp4.

Non-video files — cover.jpg, backdrop.jpeg, and poster.jpg scattered at root and inside subdirectories to exercise the non-video detection path.

Output directories

Empty demo/movies/ and demo/series/ dirs (.gitkeep) act as the move targets so users can run a full Scan → Proceed cycle without touching their real media.

Docs

• demo/README.md — contents table, expected scan results, .env wiring, and git restore demo/ reset instructions.
• Root README.md — "Try the demo first" callout added to Quick Start.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create demo dataset</issue_title>
<issue_description>This should include example video files and structures. The video files can be empty, or very small.</issue_description>

Comments on the Issue (you are @copilot in this section)

@colinmakerofthings - Create a list of placeholder video files to use for demos. - Videos can be empty files. - Use a range of extensions and naming conventions. - Use movies with expired copyright - Gulliver's Travels (1939), The Little Shop of Horrors (1960), Night of the Living Dead (1968), The Stranger (1946), White Zombie (1932). - For TV Series, use The Lone Ranger, Season 1, episodes 1-3 - Add in a few empty jpegs to highlight the non-video file functionality.

• Fixes Create demo dataset #22

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[colinmakerofthings]

Closes #29