chore: revert Lavalink timeout to 30s, add PMD + stricter checkstyle

- LavalinkManager: httpTimeout back to 30s (stagger delays are the real fix)
- checkstyle: comprehensive ruleset from LoParkour (200-line files, complexity, naming)
- PMD: ruleset with CognitiveComplexity, CloseResource, TooManyMethods etc
- Both tools run with ignoreFailures=true (warnings only, don't block build)

build.gradle

@@ -2,6 +2,7 @@ plugins {
     id 'java'
     id 'application'
     id 'checkstyle'
+    id 'pmd'
     alias(libs.plugins.spotbugs)
     id 'com.diffplug.spotless' version '6.25.0'
 }
@@ -78,6 +79,12 @@ checkstyle {
     ignoreFailures = true
 }
 
+pmd {
+    ruleSets = []
+    ruleSetFiles = files("${rootDir}/config/pmd/ruleset.xml")
+    ignoreFailures = true
+}
+
 spotbugs {
     excludeFilter = file("${rootDir}/config/spotbugs/exclude.xml")
     ignoreFailures = false