feat: classify provider_disabled 503 as non-retryable (#25800)

Builds on top of https://github.com/coder/coder/pull/25794

Adds a new `provider_disabled` error classification in `chatd` with the
corresponding plumbing to classify it as non-retryable. Also adds a
story for how this particular error kind is displayed in the UI.

coderd/apidoc/swagger.json

@@ -14848,7 +14848,8 @@
 				"auth",
 				"config",
 				"usage_limit",
-				"missing_key"
+				"missing_key",
+				"provider_disabled"
 			],
 			"x-enum-varnames": [
 				"ChatErrorKindGeneric",
@@ -14859,7 +14860,8 @@
 				"ChatErrorKindAuth",
 				"ChatErrorKindConfig",
 				"ChatErrorKindUsageLimit",
-				"ChatErrorKindMissingKey"
+				"ChatErrorKindMissingKey",
+				"ChatErrorKindProviderDisabled"
 			]
 		},
 		"codersdk.ChatFileMetadata": {