Wires the per-user MCP custom header values store from migration 000510
through the data layer: sqlc queries, dbauthz wrappers (ActionRead/UpdatePersonal
mirroring ExternalAuthLink), dbcrypt envelope encryption around header_values,
dbgen fakes, and dbmock + dbmetrics regeneration.
Adds CustomHeadersUserKeys to InsertMCPServerConfig and UpdateMCPServerConfig
so the admin-configured set of user-set header names round-trips with the
existing custom_headers JSON.
Subsequent commits will surface this via the SDK, HTTP handlers, runtime
overlay in chatd, and the admin + user-settings UI.
Steven Masley
9c30cf886e