fix(lint,command,scheduler): lpk alias, ReturnCount/IllegalCatch triage, scheduler facade

- command: replace /lp alias with /lpk (LuckPerms conflict, p.144);
  parkour alias kept; docs/changelog/javadoc updated
- lint p.169: restructure last 69 void early-returns into if-blocks and
  helpers; ReturnCount is now an error gate (0 violations)
- lint p.170: Throwable->RuntimeException on 3 boundaries; narrow 5
  catches to concrete types; document 14 intentional boundary catches
- scheduler p.21: add runTimerAsync to the facade (Bukkit + Folia
  backends); MetricsCacheStore and duels go through the facade, no
  BukkitRunnable/Bukkit.getScheduler outside scheduler/ (archunit
  freeze-store emptied); drop the unverified Folia badge from README
- tracker: mark p.26-29/32-33 done (fixed in fea15e6, verified)

config/checkstyle/checkstyle.xml

@@ -68,7 +68,7 @@
 
         <module name="ReturnCount">
             <property name="max" value="5"/>
-            <property name="severity" value="warning"/>
+            <property name="severity" value="error"/>
         </module>
 
         <module name="AvoidStarImport"/>