feat: add Discord NetCord gateway worker

Add a separate GmRelay.DiscordBot worker using NetCord Gateway with startup token validation, PostgreSQL datasource registration, slash-command setup, component interaction service registration, and lifecycle logging.

Wire the Discord service through Aspire AppHost, Docker Compose, PR checks, deploy image build/push/scan/pull steps, README docs, and synchronized version 2.2.0.

Add TDD coverage for project isolation, token validation, startup wiring, runtime wiring, and version synchronization.

Bump version -> 2.2.0

compose.yaml

@@ -49,7 +49,7 @@ services:
         crond -f
 
   bot:
-    image: git.codeanddice.ru/toutsu/gmrelay-bot:2.1.1
+    image: git.codeanddice.ru/toutsu/gmrelay-bot:2.2.0
     restart: always
     depends_on:
       db:
@@ -66,8 +66,20 @@ services:
       timeout: 5s
       retries: 3
 
+  discord:
+    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:2.2.0
+    restart: always
+    depends_on:
+      db:
+        condition: service_healthy
+    environment:
+      - "ConnectionStrings__gmrelaydb=Host=db;Port=5432;Database=gmrelay_db;Username=gmrelay;Password=${POSTGRES_PASSWORD:?Set POSTGRES_PASSWORD in .env}"
+      - "Discord__Token=${DISCORD_BOT_TOKEN:?Set DISCORD_BOT_TOKEN in .env}"
+    networks:
+      - gmrelay
+
   web:
-    image: git.codeanddice.ru/toutsu/gmrelay-web:2.1.1
+    image: git.codeanddice.ru/toutsu/gmrelay-web:2.2.0
     restart: always
     depends_on:
       db: