Fix and Expand Oni Demon Tail Markings

[rebaserHEAD]

About the PR

Fixes the Demon Tail markings on Oni, which were rendering as broken fragments, and rounds the set out with the animated and plain variants from the original ADT source.

Why / Balance

The "ADT Markings (#49)" import brought these demon tails over as a single sprite layer, but in the ADT source each tail is two layers: a base silhouette (parts.rsi:tail) under a pattern/recolor overlay (tails_of_demons.rsi). Only the overlay was imported, so in-game there was no tail underneath the pattern and players saw scattered detail pixels. We re-sourced the base silhouette and the animated sheets from AdventureTimeSS14 (lunalita, CC-BY-SA-3.0, same as the rest of the sheet), added them to custom.rsi, and rewired the markings to layer base + overlay the way ADT intended. Purely cosmetic customization, no balance impact.

Media

Requirements

• I have read relevant guidelines/documentation to this PR found on our devwiki.
• I have added media to this PR or it does not require an ingame showcase.
• I can confirm this PR contains either no AI-generated content, or AI-generated content that meets our guidelines.

How to test

1. Open the character editor on an Oni.
2. In the Tail marking slot, select Demon Tail 1 / Long / Up and confirm each renders a full, coherent tail (previously broken).
3. Select the (Animated) variants and confirm the tail wags through its cycle, with the pattern staying aligned to the silhouette.
4. Select the Plain and Plain (Animated) variants and confirm a single-color tail with no pattern overlay.
5. Spot-check all four facings, and that the patterned tails expose two color layers (Tail + Pattern).

Breaking changes

None. The existing marking ids are unchanged, so saved characters keep their selections.

[github-actions]

RSI Diff Bot; head commit 074d64c merging into ac55186
This PR makes changes to 1 or more RSIs. Here is a summary of all changes:

Resources/Textures/_ADT/Mobs/Customization/Demon/custom.rsi

State	Old	New	Status
demon_tail_base			Added
demon_tail_waggin			Added
long_waggin			Added
tail_waggin			Added
up_waggin			Added

[chadosmen1]

hello lead spriter here I am going to be reviewing this sprite to see if its fit to be added

[rebaserHEAD]

hello lead spriter here I am going to be reviewing this sprite to see if its fit to be added

What are we thinking, boss?

[DDrakov]

It works and good enough