Phase 4: veins in every chunk, drops for the mobs the island lacks

Ore veins: make_world.py loads the island again row by row until
Regenerating Ore Veins has filled every chunk (/cobblesurvival veins
unfilled), cave tiers sit at their biome's depths, small zones get denser
veins, showcase veins are full size. The world report checks surface
tiers against the zone grid, cave tiers within two biome cells of their
cave, and fails on unfilled chunks; the template passes (37,689 chunks).

Drops: tools/drop_audit.py checks every creature drop a recipe or brewing
needs (docs/pokemon-drops.md). Blaze rods, ghast tears, breeze rods,
shulker shells and nether stars now drop from Pokemon through species
additions (self-test drop_additions_apply). The field guide counts vanilla
mobs as absent, applies species additions and reads the veins as sources.

Cobblebase tried (loads, self-tests pass) and left out until Adrian
decides its scope. Phase 4 checklist with the open questions.

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

tools/fieldguide/world.py

@@ -515,6 +515,16 @@ class Island:
                     self._add_mob(mob, "special", note, st)
             elif kind == "item":
                 self.item_mobs[mob] = (req, note)
+        # The companion mod lets only Cobblemon's entities join a world (world/OnlyPokemon.kt), apart from the
+        # entity type tag cobblesurvival:allowed_vanilla_mobs; every other mob never appears, whatever spawns it.
+        self.allowed_mobs = self.tags["entity_type"].resolve("#cobblesurvival:allowed_vanilla_mobs")
+        for mob, entries in self.mobs.items():
+            if not self.mob_allowed(mob):
+                for e in entries:
+                    e["status"] = "unavailable"
+
+    def mob_allowed(self, mob):
+        return mob.startswith("cobblemon:") or mob in self.allowed_mobs
 
     def _add_mob(self, mob, kind, where, status):
         lst = self.mobs.setdefault(mob, [])