feat: admin/chef/player permission model + leaderless teams + setleader

Commands:
- Drop all short aliases (c/i/t/j/vis/disband/...) — long names only.
- Every /core team <action> now has a crcore.team.<action> permission.
- Three-tier model:
  * Admin (perm only): create, delete, setleader, score
  * Chef (perm + chef-check in execute): add, remove, transfer, visibility, setspawn
  * Player (perm): join, leave, info, list, top
- delete now takes <team> as argument (admin); no more chef-disband shortcut.

New /core team setleader <team> <player>:
- Admin assigns or replaces a team's leader.
- More permissive than transfer: target may not yet be a member (auto-add),
  and works on leaderless teams.

Leaderless teams:
- Team.leaderId is now nullable.
- getLeaderId() and getLeader() return Optional<...>.
- hasLeader() and isLeader(UUID) helpers added.
- New constructors Team(id, name, tag, color [, visibility]) for leaderless.
- TeamService.createTeam overloads without leaderId.
- TeamService.setLeader(teamId, playerId): assigns/replaces leader (auto-adds
  as member if needed). Fires TeamLeadershipTransferEvent with optional old.
- TeamLeadershipTransferEvent.getOldLeaderId() returns Optional<UUID>.
- SqliteTeamRepository: leader_id column no longer NOT NULL.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/diagrams/team-class-diagram.puml

@@ -101,17 +101,24 @@ package "fr.luc.crcore.team" {
     - name: String
     - tag: String
     - color: TeamColor
-    - leaderId: UUID
+    - leaderId: UUID *(nullable)*
     - visibility: TeamVisibility
     - members: Set<TeamMember>
     - scores: Map<String, Integer>
     - spawnPoint: Location
     --
+    + Team(id, name, tag, color)             ' leaderless, PRIVATE
+    + Team(id, name, tag, color, visibility) ' leaderless
+    + Team(id, name, tag, color, leaderId)   ' with leader, PRIVATE
+    + Team(id, name, tag, color, leaderId, visibility)
+    --
     + getName(): String
     + getTag(): String
     + getColor(): TeamColor
-    + getLeaderId(): UUID
-    + getLeader(): TeamMember
+    + getLeaderId(): Optional<UUID>
+    + getLeader(): Optional<TeamMember>
+    + hasLeader(): boolean
+    + isLeader(playerId): boolean
     + getVisibility(): TeamVisibility
     + setVisibility(v): void
     + isPublic(): boolean
@@ -121,7 +128,8 @@ package "fr.luc.crcore.team" {
     + size(): int
     + addMember(playerId): TeamMember
     + removeMember(playerId): boolean
-    + transferLeadership(newLeaderId): void
+    + transferLeadership(newLeaderId): void     ' strict: chef→chef
+    + setLeader(newLeaderId): void              ' permissive: assign
     --
     + getScore(name): int
     + hasScore(name): boolean
@@ -157,12 +165,16 @@ package "fr.luc.crcore.team" {
   }
 
   interface TeamService {
-    + createTeam(name, tag, color, leaderId, [visibility]): Team
+    + createTeam(name, tag, color): Team                  ' leaderless, PRIVATE
+    + createTeam(name, tag, color, visibility): Team      ' leaderless
+    + createTeam(name, tag, color, leaderId): Team
+    + createTeam(name, tag, color, leaderId, visibility): Team
     + dissolveTeam(teamId): boolean
     + addMember(teamId, playerId): boolean
     + removeMember(teamId, playerId): boolean
     + joinTeam(teamId, playerId): boolean
-    + transferLeadership(teamId, newLeaderId): boolean
+    + transferLeadership(teamId, newLeaderId): boolean    ' strict: chef→chef
+    + setLeader(teamId, newLeaderId): boolean             ' permissive (admin)
     + setVisibility(teamId, visibility): void
     --
     + addScore(teamId, name, delta): int