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>

.gitignore

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+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+.kotlin
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+.idea/workspace.xml
+.idea/shelf/
+.idea/tasks.xml
+.idea/usage.statistics.xml
+.idea/dictionaries
+.idea/httpRequests
+.idea/dataSources/
+.idea/dataSources.ids
+.idea/dataSources.local.xml
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store