docs: organize diagrams to mirror code layout (util/ + features/)

Move flat docs/diagrams/*.puml into a hierarchy matching the source
package structure:

  docs/diagrams/
  ├── bootstrap-sequence.puml         (cross-cutting)
  ├── events-diagram.puml             (cross-feature)
  ├── util/
  │   ├── command-class-diagram.puml
  │   ├── database-diagram.puml
  │   ├── messages-class-diagram.puml
  │   ├── broadcasts-class-diagram.puml
  │   └── gui-class-diagram.puml
  └── features/
      ├── team/
      │   ├── team-class-diagram.puml
      │   ├── team-config-class-diagram.puml
      │   ├── builtin-commands-diagram.puml
      │   ├── team-create-sequence.puml
      │   ├── team-create-activity.puml
      │   └── team-join-sequence.puml
      ├── player/
      │   └── player-class-diagram.puml
      └── moderation/
          └── moderation-class-diagram.puml

README.md diagram index split into 4 sections (overview, util,
features/team, features/player, features/moderation) for readability;
all links updated. features.md auto-updated by sed for the new paths.

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

docs/diagrams/util/database-diagram.puml

@@ -0,0 +1,86 @@
+@startuml database-diagram
+title CR-Core — Database (SQLite wrapper)
+
+skinparam classAttributeIconSize 0
+hide empty members
+
+package "fr.luc.crcore.util.database" {
+
+  class Database {
+    - connection: Connection
+    + Database(file: File)
+    + execute(sql, params...): void
+    + update(sql, params...): int
+    + queryOne(sql, mapper, params...): Optional<T>
+    + query(sql, mapper, params...): List<T>
+    + inTransaction(block: Runnable): void
+    + table(name: String): TableBuilder
+    + tableExists(name: String): boolean
+    + getConnection(): Connection
+    + close(): void
+  }
+  Database ..|> "java.lang.AutoCloseable"
+
+  class TableBuilder {
+    - database: Database
+    - name: String
+    - columns: List<ColumnDef>
+    - ifNotExists: boolean
+    + ifNotExists(): TableBuilder
+    + column(name, type): ColumnDef
+    + create(): void
+  }
+
+  class "TableBuilder.ColumnDef" as ColumnDef {
+    - name: String
+    - type: ColumnType
+    - primaryKey: boolean
+    - notNull: boolean
+    - unique: boolean
+    - defaultValue: String
+    + primaryKey(): ColumnDef
+    + notNull(): ColumnDef
+    + unique(): ColumnDef
+    + defaultValue(expr: String): ColumnDef
+    + column(name, type): ColumnDef
+    + create(): void
+  }
+
+  enum ColumnType {
+    INTEGER
+    REAL
+    TEXT
+    BLOB
+    BOOLEAN
+    UUID
+    --
+    + getSqlType(): String
+  }
+
+  interface "RowMapper<T>" as RowMapper {
+    + map(rs: ResultSet): T
+  }
+
+  class DatabaseException
+  DatabaseException --|> RuntimeException
+
+  Database "1" *-- "*" TableBuilder : creates
+  TableBuilder "1" *-- "*" ColumnDef : contains
+  ColumnDef --> ColumnType : type
+  Database ..> RowMapper : uses
+  Database ..> DatabaseException : throws
+}
+
+note right of Database
+  Repositories SQLite de CR-Core
+  (SqliteTeamRepository,
+   SqlitePlayerProfileRepository)
+  utilisent Database pour
+  persister state team/player.
+
+  Les plugins de jeu utilisent
+  Database.table(...) pour
+  créer leurs tables custom.
+end note
+
+@enduml