docs: merge the Fleet docs into backend/fleet/README.md, add TODO.md, unify the Backend compose, fix stale references [CI SKIP]

compose.yaml

@@ -12,7 +12,7 @@ services:
       MoShiro__InitialAdminUser: ${MOSHIRO_ADMIN_USER:-admin}
       MoShiro__InitialAdminPassword: "${MOSHIRO_ADMIN_PASSWORD:?Set MOSHIRO_ADMIN_PASSWORD in the environment}"
     volumes:
-      - moshiro-data:/data
+      - moshiro-backend-data:/data
     read_only: true
     tmpfs:
       - /tmp:rw,noexec,nosuid,size=64m,mode=1777
@@ -23,4 +23,5 @@ services:
     stop_grace_period: 30s
 
 volumes:
-  moshiro-data:
+  moshiro-backend-data:
+    name: moshiro-backend-data