feat: add redirection support for demonlist via /demonlist/levelid/<level_id>

[jhk1090]

Adding a redirection route for /demonlist/levelid/<level_id>. This behaves identically to the current /demonlist/permalink/<demon_id> behavior (redirecting to the current position).

It would improve developer and user experience, making it easier to share or link to specific demons programmatically.

Why this is needed:

1. Fixes Broken Links due to Rank Fluctuations: Currently, referencing a demon by its list position (e.g., /demonlist/1/) is unreliable because the leaderboard is dynamic. When new top demons are added or placements shift, the old URL points to a completely different level.
2. True Immutable Permalink: In contrast to internal demon_id, Geometry Dash's level_id is an immutable, universally recognized identifier within the community. Utilizing it as a redirection route guarantees a permanent, unbreakable link to a specific demon, regardless of future rank variations.

Example:

• Request: https://pointercrate.com/demonlist/levelid/127323087 (127323087 is Society's level id)
• Behavior: Redirects to the current demon page (e.g., https://pointercrate.com/demonlist/1/)

It resolves #354

License Acceptance

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