feat: initial CR-Core library (team + player + command framework)

Pure Maven library for CR Minecraft game plugins, targeting Paper 1.16.5.

Common abstractions (fr.luc.crcore.common): Identifiable, Named, ScoreHolder,
AbstractEntity, Repository<T>.

Team domain (fr.luc.crcore.team): Team entity with name/tag/color/leader/
visibility (PUBLIC|PRIVATE)/members/scores/spawn point, TeamMember,
TeamRole/TeamColor/TeamVisibility enums, TeamRanking record, TeamService with
overridable hooks (factories, validations, lifecycle events), in-memory
repository, dedicated exception hierarchy.

Player domain (fr.luc.crcore.player): PlayerProfile with named scores per
player, PlayerProfileService with auto-creation, individual rankings,
exception hierarchy. Both Team and PlayerProfile implement ScoreHolder.

Command framework (fr.luc.crcore.command): Command interface,
AbstractCommand base, BaseCommand (CommandExecutor + TabCompleter), SubCommand,
CommandContext, CommandResult, ArgumentType<T> + ArgumentTypes catalogue
(STRING, INTEGER, DOUBLE, BOOLEAN, ONLINE_PLAYER, enumOf, choice).

Docs (docs/) is the single source of truth: README, setup, features,
decisions log, and 6 PlantUML diagrams (team class/sequence/activity/join,
player class, command class).

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

docs/diagrams/team-join-sequence.puml

@@ -0,0 +1,62 @@
+@startuml team-join-sequence
+title CR-Core — Player joins a public team (sequence diagram)
+
+actor Player
+participant "BaseCommand\n(TeamCommand)" as Base
+participant "SubCommand\n(TeamJoinSub)" as Sub
+participant "TeamService" as Service
+participant "TeamRepository" as Repo
+participant "Team" as Team
+
+Player -> Base : /team join <name>
+activate Base
+
+Base -> Base : route args[0]="join" → TeamJoinSub
+Base -> Sub : execute(ctx)
+activate Sub
+
+Sub -> Service : getTeamByName(name)
+activate Service
+Service -> Repo : findByName(name)
+activate Repo
+Repo --> Service : Optional<Team>
+deactivate Repo
+Service --> Sub : Optional<Team>
+deactivate Service
+
+alt team not found
+  Sub --> Base : CommandResult.failure("Team not found")
+else team found
+  Sub -> Service : joinTeam(team.id, playerId)
+  activate Service
+
+  Service -> Service : validateJoinable(team, playerId)
+  alt team is PRIVATE
+    Service --> Sub : throw TeamAccessException
+    Sub --> Base : CommandResult.failure(ex.message)
+  else player already in a team
+    Service --> Sub : throw TeamAccessException
+    Sub --> Base : CommandResult.failure(ex.message)
+  else allowed
+    Service -> Team : addMember(playerId)
+    activate Team
+    Team --> Service : member
+    deactivate Team
+    Service -> Repo : save(team)
+    activate Repo
+    Repo --> Service : team
+    deactivate Repo
+    Service -> Service : onMemberAdded(team, member)
+    Service -> Service : onPlayerJoined(team, member)
+    Service --> Sub : true
+    Sub --> Base : CommandResult.success("Joined " + team.name)
+  end
+  deactivate Service
+end
+
+deactivate Sub
+Base -> Base : handleResult → sender.sendMessage
+Base --> Player : reply
+deactivate Base
+
+@enduml