New sprites by skai for post-game elements

New sprites by skai

Vine, by Patashu, in Chapter R (WIP)

Yet another new contributor, skai! So far she's made some sprites for post-game elements (replacing my shoddy devart) and a few custom puzzles and I'm excited to see some more in the future.

Changelogs follow:

**v19.5 (8th July 2025):**

* New graphics for Floorboards, Grates, Phase Wall Green Even/Odd and Checkpoints. Added skai to Credits.

* Time Colours Purple/Blurple/Yellow are renamed Crimson/Teal/Purple, respectively. Renamed The Yellow Pit and its (Remix) to The Purple Pit.

* Level Editor Instructions now says 'Clear Level'.

* Fix that Chapter 2?'s dark background persisted after pressing 'Community Levels'.

* Level Editor tile picker: Give the other Repair Stations names.

* Chapter R (WIP): Add Blue Ghost, Anchor Lock, Empty Tower, Vine, Vine [VAR1], Pushing It Blue, Makeshift Ladder. Update Dig, Mechanical Arm.

* The Cutting Room Floor: Rename Acrobatics? [VAR1] to Isometric Exercise.

* Formless Exploration: Add Dead Air [Act 2].

* Journeyless Fragments: Open in Community Levels. Add Kelrn Ocrwh, Kelrn Ocryt, Normality, Maneuver.

* Unit test mode is 10x faster. I didn't have to make any performance improvements or do anything technically difficult, I just wanted it to be 10x faster, so now it is.