Phase 6 done: see-through cores, faint on sacrifice and rebirth; Phase 7 design

Adrian (2026-11-02): the cores should be transparent so the Pokémon
shows; the Pokémon's death sound when a sacrifice is made or a rebirth
ends; then start the next phase (Phase 6 approved).

- Cores drawn as a solid frame around tinted glass, rendered
  translucent, no occlusion (tools/machine_assets.py).
- The shown Pokémon plays Cobblemon's faint animation and its cry
  pitched down (Cobblemon has no death sounds), vanishes after 2 s; a
  reborn Pokémon then shows in its new form. Tests check the new form.
- Phase 7 decisions (every guardian gets area attacks, Groudon for the
  Basalt Furnace, Giratina replaces the Ender Dragon, dying or leaving
  the arena loses) and design in docs/design.md; README status.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/checklists/phase-6.md

@@ -30,6 +30,8 @@ Elsewhere, creative mode gives the cores in the Functional Blocks tab; each has
 
 - [ ] Use a bare core (third row): ghost blocks show its shell for ten seconds, and chat lists what's missing. Place a new core anywhere: the same.
 - [ ] Hover a core in the inventory: the tooltip says what it does and what its shell is made of.
+- [ ] Look at a working machine from the front: the core is see-through (frame and tinted glass), the Pokémon shows behind it.
+- [ ] Sacrifice a Pokémon, or finish a rebirth: the Pokémon in the chamber faints with its cry pitched down, then disappears (a reborn one comes back in its new form).
 
 - [ ] Build a Heat Core shell of bricks with glass in a side window, send out a Fire type and use the core: the Pokémon stands in the chamber, small enough to fit, and doesn't move. **Does it look right?** (the roadmap asks you to confirm this)
 - [ ] Put a furnace against the outside of that shell, a hopper with raw iron above it and a hopper with a chest below: the iron cooks without fuel, faster with a stronger Pokémon (speed doubled on 2026-11-02: 7.4× at Lv 50), and ends in the chest.
@@ -41,5 +43,7 @@ Elsewhere, creative mode gives the cores in the Functional Blocks tab; each has
 
 ## Ask Adrian
 
+**Phase 6 approved 2026-11-02** (after the see-through cores and the faint: "After that, you can begin with the next phase"). Numbers, casings and recipes stay placeholders.
+
 - Does the Pokémon in the chamber look right (size, place, facing out through the core's side)?
 - All numbers, casings and recipes are placeholders (`docs/balance.md`).