Phase 3: Alpha guardians, one per zone, back 5 hours after a defeat

- Companion mod (zone/Guardians.kt): each zone's guardian stands at the
  zone's sample point, appears when a player is within 96 blocks, stays
  within 24 blocks, is uncatchable and half again as big. Beating it in a
  battle gives every player in the battle its drops; it returns after 5
  hours of game time (Adrian: fixed spots, 5 hours). State lives in the
  world save; /cobblesurvival guardians lists it.
- tools/zone_spawns.py writes data/cobblesurvival/guardians/<zone>.json:
  the strongest walking (or swimming) Pokemon of the zone at band top + 5,
  with the drops from world/zones.json. Boss drops follow Adrian's rule:
  Icy Rocks before Sunscorch, Heat Rocks before Frostpeak.
- Goat Fur and Hoglin Hide recipes make 8 per rock, so one guardian's 3
  rocks pay for one full insulating set.
- Self-test guardian_appears_and_returns; hazard tests cleaned up; the
  zone generator reads Cobblemon's own entries from the field guide's
  hidden_spawns.

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

docs/checklists/phase-3.md

@@ -17,7 +17,9 @@ Open `build/zone-map.png` (the island coloured by zone) and read the draft in `d
 
 - **Heat and cold** (step 5, Cold Sweat). Automated: `cold_needs_fur`, `heat_needs_hide` and `lowlands_are_mild` on the island in `tools/quick_check.py`.
 
-Still to come: Alpha guardians with the boss drops that help the next zone (including the Heat and Icy Rocks), the Mire's poison, soft level pressure, flyers.
+- **Alpha guardians** (step 4). One per zone at a fixed spot, back 5 hours after being beaten; drops help with the next zone (`docs/zone-species.md` lists them). Automated: `guardian_appears_and_returns`.
+
+Still to come: the Mire's poison (and the wading gear the Westmarch and Jungle guardians should drop for it), soft level pressure, flyers.
 
 ## In-game
 
@@ -27,3 +29,4 @@ Still to come: Alpha guardians with the boss drops that help the next zone (incl
 - [ ] **Frostpeak cold:** walk onto the jagged peaks without gear: Cold Sweat's thermometer drops and after a minute or so you take damage (not during the first 5 minutes of a new world: grace period). In the fur set (Goat Fur from 8 wool + 1 Heat Rock) you last many minutes.
 - [ ] **Sunscorch heat:** the desert at noon overheats you in a couple of minutes; at night it's fine. The hide set (Hoglin Hide from 8 leather + 1 Icy Rock) or a Fire Resistance potion keeps you going.
 - [ ] **Lowlands:** a night in Southwold or on Button Isle without gear never gets dangerous.
+- [ ] **Guardians:** `/cobblesurvival guardians` (operator) lists each zone's guardian and spot. Walk there: a big Pokémon appears, can't be caught, and beating it puts its drops in your inventory with a gold message. It's gone for 5 hours of play.