chore: downgrade compile target to Java 11

Uses <release>11</release> in maven-compiler-plugin (recommended over
source/target to guarantee bytecode and API surface match Java 11).

Code changes to drop Java 12-16 features:
- records (TeamRanking, PlayerRanking, internal tuples in
  SqliteTeamRepository) become hand-written immutable classes; same
  accessor names (rank()/team()/score()/...) so call sites are unchanged.
- instanceof X x pattern matching becomes classic instanceof + cast in
  CommandContext.requirePlayer and Database.normalize.
- switch expressions with -> arrows become classic switch + break, or
  if/else chains, in BaseCommand.handleResult, ArgumentTypes.BOOLEAN and
  TeamScoreSubCommand.execute.

docs/setup.md, features.md and decisions.md updated to reflect Java 11.

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

pom.xml

@@ -13,8 +13,13 @@
     <description>Reusable core library for CR Minecraft game plugins (teams, players, scores, commands, events, SQLite persistence).</description>
 
     <properties>
-        <maven.compiler.source>16</maven.compiler.source>
-        <maven.compiler.target>16</maven.compiler.target>
+        <!--
+            On utilise <release> plutôt que <source>+<target> pour garantir
+            que les références à des API ne sont pas accidentellement plus
+            récentes que Java 11 (ex. List.copyOf en Java 10+ : OK ;
+            Stream.toList en Java 16+ : refusé par javac).
+        -->
+        <maven.compiler.release>11</maven.compiler.release>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <sqlite.version>3.45.3.0</sqlite.version>
     </properties>
@@ -83,8 +88,7 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.11.0</version>
                 <configuration>
-                    <source>${maven.compiler.source}</source>
-                    <target>${maven.compiler.target}</target>
+                    <release>${maven.compiler.release}</release>
                 </configuration>
             </plugin>
 
@@ -121,7 +125,7 @@
                 <artifactId>maven-javadoc-plugin</artifactId>
                 <version>3.6.3</version>
                 <configuration>
-                    <source>${maven.compiler.source}</source>
+                    <source>${maven.compiler.release}</source>
                     <doclint>none</doclint>
                     <quiet>true</quiet>
                     <encoding>UTF-8</encoding>