Phase 7: practice-boss and guardian-reset commands; steadier spawn survey

Adrian (2026-11-02): a way to force-spawn the bosses.

- /cobblesurvival boss <zone|end>: a practice copy next to you (same
  species, level, size, attacks; no drops, not the guardian's defeat).
- /cobblesurvival guardians reset <zone>: despawns the zone's guardian
  and clears its defeat, so it appears again when someone comes near
  (Guardians.reset, formerly resetForTest).
- Self-test practice_bosses_spawn.
- spawn_survey stands on the ground below trees: on a mangrove's roots
  it found no natural ground and nothing could spawn at the Mire sample.

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

mod/src/main/kotlin/dev/cobblesurvival/CobbleSurvival.kt

@@ -9,6 +9,7 @@ import dev.cobblesurvival.dev.OreVeins
 import dev.cobblesurvival.ore.BaseLoot
 import dev.cobblesurvival.ore.OreNodes
 import dev.cobblesurvival.permadeath.Permadeath
+import dev.cobblesurvival.boss.BossCommands
 import dev.cobblesurvival.boss.BossFights
 import dev.cobblesurvival.boss.EndBoss
 import dev.cobblesurvival.machine.MachineShowcase
@@ -132,7 +133,8 @@ class CobbleSurvival {
                 val lines = Guardians.status(context.source.server.overworld())
                 context.source.sendSuccess({ Component.literal(lines.joinToString("\n").ifEmpty { "no guardians loaded" }) }, false)
                 1
-            })
+            }.then(BossCommands.guardianReset()))
+            .then(BossCommands.practice())
         if (SelfTest.enabled) root.then(SelfTest.command())
         event.dispatcher.register(root)
     }