Create Deep Seas: Crush Depth

Initial public release.

- Applies Create: Deep Seas' submarine hull pressure model to **players**: exposed
  swimmers and players in breached hulls take scaling pressure damage past their
  rated depth (same math and depth scan as the hull system — no parallel physics).
- Difficulty-scaled damage, actionbar depth HUD, decompression sickness ("the bends")
  with decompression-chamber cure, and hull stress sounds when riding near rated depth.
- Gear progression: **Abyssal Adaptation** helmet enchantment (I–III), Create diving
  suit pressure bonuses, Boyle's-law backtank air drain, optional Curios curio bonuses
  (e.g. Artifacts' snorkel).
- Advancement tab with configurable, surface-relative depth thresholds.
- Fully configurable via `crush_depth-common.toml`. Server-side logic; installing on
  the client adds tooltips, HUD/death-message localization — vanilla clients can
  still join.