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/messages-class-diagram.puml

@@ -0,0 +1,63 @@
+@startuml messages-class-diagram
+title CR-Core — Messages service (class diagram)
+
+skinparam classAttributeIconSize 0
+hide empty members
+
+package "fr.luc.crcore.util.message" {
+
+  interface MessagesService {
+    + get(key, placeholderPairs...): String
+    + raw(key): String
+    + has(key): boolean
+    + set(key, template): void
+    + reload(): void
+    + loadAdditional(resourceName): void
+    + setApplyColorCodes(enabled): void
+    + isApplyColorCodes(): boolean
+    + getUserFile(): File
+  }
+
+  class YamlMessagesService {
+    - plugin: JavaPlugin
+    - defaults: Map<String, String>             ' in-memory (jar resource)
+    - messages: Map<String, String>             ' effective (defaults + user file)
+    - userFileName: String                      ' <plugin>-messages.yml
+    - userFile: File
+    - applyColorCodes: boolean
+    --
+    + YamlMessagesService(plugin: JavaPlugin)
+    --
+    - loadDefaultsFromResource(): void          ' charge crcore-messages.yml (jar)
+    - ensureUserFile(): void                    ' copie template si absent
+    - rebuildEffectiveMessages(): void          ' defaults + user file
+    - {static} flatten(section, prefix, out): void
+  }
+
+  YamlMessagesService ..|> MessagesService
+}
+
+package "fr.luc.crcore" {
+  class CRCore {
+    + messages(): MessagesService
+    # buildMessagesService(): MessagesService    ' override point
+  }
+  CRCore "1" *-- "1" MessagesService : owns
+}
+
+note bottom of YamlMessagesService
+  Modèle "un seul fichier par plugin" :
+
+  Sources en mémoire (la 2e écrase la 1ère sur clés communes) :
+    1. crcore-messages.yml          ← jar (toujours présent, fallback)
+    2. <plugin>-messages.yml        ← dataFolder (édité par l'admin)
+
+  Création du fichier user au 1er boot :
+    Priorité 1 : ressource du plugin de jeu sous le même nom
+    Priorité 2 : copie des defaults CR-Core
+
+  Placeholders : {name} via varargs key/value
+  Codes couleur : &a → §a (toggle)
+end note
+
+@enduml