ClayGrounds v0.2.4 Datapack Patch

- Adds a persistent loading boss bar showing completed generation cells out of 64.
- Adds an action-bar countdown showing generation percentage and an approximate seconds-remaining ETA.
- ETA is tied to actual completed cells rather than a blind real-time timer, so it cannot claim completion while sections are still pending.
- Replaces the tick-dispatched generator with a self-scheduling runner.
- Adds a 20-tick watchdog that restarts the runner if a schedule is lost.
- Interrupted generation resumes automatically after datapack/world reload.
- Increases the per-cell force-load settling window from 2 to 4 runner ticks while keeping only one 3x3-chunk cell force-loaded at once.
- Terrain geometry, fountain layout, combat, classes, progression, resource IDs, and existing v0.2.3 gameplay content are unchanged.
- Resource pack v0.2.3 remains fully compatible; its particle-atlas fix is already loading without ClayGrounds missing-particle warnings in the latest test.
