feat(copilot): managed profile testing and openaiCompatible provider support

- add native openaiCompatible provider type with flat baseUrl/apiKey/dialect
  config fields and declared per-model capabilities
- add admin-only probeManagedCopilotProfile GraphQL mutation that dispatches
  real probe requests against server-managed copilot profiles, reusing the
  BYOK probe engine with an AllowPrivate egress policy for self-hosted
  endpoints (Vertex profiles rejected; use workspace BYOK instead)
- expose providers.profiles app config descriptor to the admin console
- add 'AI Providers' settings group with JSON editor and per-profile Test
  action that probes declared capabilities and reports verified/failed
  status per model and operation

packages/backend/server/src/schema.gql

@@ -1448,6 +1448,33 @@ input ManageUserInput {
   name: String
 }
 
+type ManagedProfileModelProbeCheckType {
+  operation: ByokProbeOperation!
+  status: ManagedProfileProbeStatusType!
+}
+
+type ManagedProfileModelProbeType {
+  checks: [ManagedProfileModelProbeCheckType!]!
+  modelId: String!
+}
+
+input ManagedProfileProbeCheckInput {
+  modelId: String!
+  operation: ByokProbeOperation!
+}
+
+type ManagedProfileProbeResultType {
+  connection: ManagedProfileProbeStatusType!
+  definitionFingerprint: String!
+  models: [ManagedProfileModelProbeType!]!
+}
+
+type ManagedProfileProbeStatusType {
+  errorKind: String
+  kind: ByokProbeStatusKind!
+  testedAt: DateTime
+}
+
 enum McpAccessMode {
   READ_ONLY
   READ_WRITE
@@ -1631,6 +1658,11 @@ type Mutation {
   """mention user in a doc"""
   mentionUser(input: MentionInput!): ID!
   previewLicense(license: Upload!): AdminLicensePreview!
+
+  """
+  Test a server-managed copilot provider profile by dispatching real probe requests.
+  """
+  probeManagedCopilotProfile(checks: [ManagedProfileProbeCheckInput!]!, profileId: ID!): ManagedProfileProbeResultType!
   probeWorkspaceByokDraft(input: ProbeWorkspaceByokDraftInput!): WorkspaceByokProbeResultType!
   probeWorkspaceByokProfile(input: ProbeWorkspaceByokProfileInput!): WorkspaceByokProbeResultType!
   publishDoc(docId: String!, mode: PublicDocMode = Page, workspaceId: String!): DocType!