feat(deploy,runtime): wire mxaccessgw connection — endpoint, key, seed row

User confirmed the mxaccessgw client (Galaxy driver) doesn't need Windows
— only the gateway worker has that constraint. This wires the Galaxy
driver into the docker-dev fleet:

- docker-compose.yml: GALAXY_MXGW_API_KEY env var on every host service
  (admin nodes harmlessly ignore it; driver-role nodes pick it up when
  the seeded DriverInstance resolves ApiKeySecretRef=env:GALAXY_MXGW_API_KEY).
  Default value matches the key the operator provided; override via shell
  env (GALAXY_MXGW_API_KEY=... docker compose up -d) to rotate without
  editing compose.
- seed-clusters.sql: now creates a SystemPlatform Namespace
  (MAIN-galaxy, urn:zb:docker-dev:galaxy) plus a GalaxyMxGateway
  DriverInstance (MAIN-galaxy-mxgw) in the MAIN cluster pointing at
  http://10.100.0.48:5120 with UseTls=false. Idempotent via IF NOT EXISTS.
- DriverInstanceActor.ShouldStub: clarified the doc comment — only the
  legacy "Galaxy" type name and "Historian.Wonderware" are Windows-only;
  the v2 "GalaxyMxGateway" driver is .NET 10 cross-platform (gRPC to an
  external gateway) and is NOT stubbed.
- README: documents the final operator step — sign in, click "Deploy
  current configuration" on /deployments to materialise the seeded
  Galaxy driver into a running gRPC connection. Raw DriverInstance rows
  don't spawn drivers on their own; the v2 lifecycle requires a sealed
  Deployment first.

docker-dev/docker-compose.yml

@@ -98,6 +98,7 @@ services:
       Security__Jwt__Issuer: "otopcua-dev"
       Security__Jwt__Audience: "otopcua-dev"
       Authentication__Ldap__DevStubMode: "true"
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
 
   admin-b:
     <<: *otopcua-host
@@ -114,6 +115,7 @@ services:
       Security__Jwt__Issuer: "otopcua-dev"
       Security__Jwt__Audience: "otopcua-dev"
       Authentication__Ldap__DevStubMode: "true"
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
 
   driver-a:
     <<: *otopcua-host
@@ -125,6 +127,9 @@ services:
       Cluster__PublicHostname: "driver-a"
       Cluster__SeedNodes__0: "akka.tcp://otopcua@admin-a:4053"
       Cluster__Roles__0: "driver"
+      # Resolved at runtime by GalaxyDriver.ResolveApiKey when a DriverInstance's
+      # Gateway.ApiKeySecretRef = "env:GALAXY_MXGW_API_KEY".
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
     ports:
       - "4840:4840"
 
@@ -138,6 +143,7 @@ services:
       Cluster__PublicHostname: "driver-b"
       Cluster__SeedNodes__0: "akka.tcp://otopcua@admin-a:4053"
       Cluster__Roles__0: "driver"
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
     ports:
       - "4841:4840"
 
@@ -162,6 +168,7 @@ services:
       Security__Jwt__Issuer: "otopcua-dev"
       Security__Jwt__Audience: "otopcua-dev"
       Authentication__Ldap__DevStubMode: "true"
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
     ports:
       - "4842:4840"
 
@@ -184,6 +191,7 @@ services:
       Security__Jwt__Issuer: "otopcua-dev"
       Security__Jwt__Audience: "otopcua-dev"
       Authentication__Ldap__DevStubMode: "true"
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
     ports:
       - "4843:4840"
 
@@ -205,6 +213,7 @@ services:
       Security__Jwt__Issuer: "otopcua-dev"
       Security__Jwt__Audience: "otopcua-dev"
       Authentication__Ldap__DevStubMode: "true"
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
     ports:
       - "4844:4840"
 
@@ -227,6 +236,7 @@ services:
       Security__Jwt__Issuer: "otopcua-dev"
       Security__Jwt__Audience: "otopcua-dev"
       Authentication__Ldap__DevStubMode: "true"
+      GALAXY_MXGW_API_KEY: "${GALAXY_MXGW_API_KEY:-mxgw_otopcua__UY_NKlBl3vWuZt8HD7usfZsU76eibMKB6CufwzabUI}"
     ports:
       - "4845:4840"