add @tailrec wherever possible

modules/common/src/main/base/Levenshtein.scala

@@ -12,6 +12,7 @@ object Levenshtein {
         val i = j - dd
         ((i - (threshold - 1)) max 0) until (1 + ((i + t) min a.length))
       }
+      @scala.annotation.tailrec
       def loop(j: Int, prev: Array[Int], prevr: Range, next: Array[Int]): Int = {
         if (j > b.length) prev.last
         else {

modules/lobby/src/main/LobbyTrouper.scala

@@ -160,6 +160,7 @@ final private class LobbyTrouper(
   private def findCompatible(hook: Hook): Option[Hook] =
     findCompatibleIn(hook, HookRepo findCompatible hook)
 
+  @scala.annotation.tailrec
   private def findCompatibleIn(hook: Hook, in: Vector[Hook]): Option[Hook] =
     in match {
       case Vector() => none

modules/puzzle/src/main/Line.scala

@@ -11,6 +11,7 @@ case class Retry(move: String)              extends Line
 object Line {
 
   def minDepth(lines: Lines): Int = {
+    @scala.annotation.tailrec
     def walk(subs: Vector[(Lines, Int)]): Option[Int] =
       subs match {
         case Vector() => none

modules/study/src/main/ChapterMaker.scala

@@ -168,6 +168,7 @@ final private class ChapterMaker(
     s"""$escapedDomain/(\\w{8,12})"""
   }.r.unanchored
 
+  @scala.annotation.tailrec
   private def parseGame(str: String): Fu[Option[Game]] =
     str match {
       case s if s.length == Game.gameIdSize => gameRepo game s

modules/tournament/src/main/arena/ArenaSheet.scala

@@ -113,6 +113,7 @@ object Sheet {
     scores.headOption.exists(_.res == ResWin) &&
       scores.lift(1).exists(_.res == ResWin)
 
+  @scala.annotation.tailrec
   private def isDrawStreak(scores: List[Score]): Boolean =
     scores match {
       case Nil => false