Add unmanaged skill provenance to agent skills

Expose adapter-discovered user-installed skills with provenance metadata, share persistent skill snapshot classification across local adapters, and render unmanaged skills as a read-only section in the agent skills UI.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/adapters/types.ts

@@ -16,6 +16,7 @@ export type {
   AdapterEnvironmentTestContext,
   AdapterSkillSyncMode,
   AdapterSkillState,
+  AdapterSkillOrigin,
   AdapterSkillEntry,
   AdapterSkillSnapshot,
   AdapterSkillContext,