fix: avoid an errant license warning banner on new deployments that d… (#26239)

Problem: CODER_AI_GATEWAY_ENABLED defaulted to true, which both started
the in-memory gateway and enabled the licensed FeatureAIBridge. As a
result, deployments that never configured AI Gateway saw a spurious "AI
Governance add-on is required" warning whenever they had an older
(non-add-on) Premium license, since the feature was enabled-and-entitled
by default.

Fix: Decouple "external AI Gateway API enabled" from "in-memory daemon
running," so the external/licensed surface is off by default while Coder
Agents retain access by default.

codersdk/deployment.go

@@ -1805,7 +1805,7 @@ func (c *DeploymentValues) Options() serpent.OptionSet {
 		Flag:        "ai-gateway-enabled",
 		Env:         "CODER_AI_GATEWAY_ENABLED",
 		Value:       &c.AI.BridgeConfig.Enabled,
-		Default:     "true",
+		Default:     "false",
 		Group:       &deploymentGroupAIGateway,
 		YAML:        "enabled",
 	}
@@ -4191,7 +4191,7 @@ Write out the current server config as YAML to stdout.`,
 			Flag:        "aibridge-enabled",
 			Env:         "CODER_AIBRIDGE_ENABLED",
 			Value:       &c.AI.BridgeConfig.Enabled,
-			Default:     "true",
+			Default:     "false",
 			Group:       &deploymentGroupAIBridge,
 			YAML:        "enabled",
 			Hidden:      true,