feat(apiproxy): workspace.archiveSession RPC and archived-sessions frame

workspace.archiveSession answers the full updated archive set;
workspace.list carries the set as the reconnect baseline; the host
stream pushes host/archived-sessions-changed full snapshots from the
domain/changed global-put branch (same posture as workspace-changed).
Unknown sessions map to the existing session-not-found code.

packages/host/apiproxy/src/fetch/handler.ts

@@ -33,6 +33,7 @@ import {
   hostPickDirectoryRequestSchema,
 } from '../api/host.schema.ts'
 import {
+  workspaceArchiveSessionRequestSchema,
   workspaceCreateRequestSchema,
   workspaceDeleteRequestSchema,
   workspaceInsertSessionBeforeRequestSchema,
@@ -96,6 +97,7 @@ const UNARY_ROUTES: UnaryRoutes = {
   'workspace.rename': { schema: workspaceRenameRequestSchema, invoke: (api, r) => api.workspace.rename(r) },
   'workspace.delete': { schema: workspaceDeleteRequestSchema, invoke: (api, r) => api.workspace.delete(r) },
   'workspace.insertSessionBefore': { schema: workspaceInsertSessionBeforeRequestSchema, invoke: (api, r) => api.workspace.insertSessionBefore(r) },
+  'workspace.archiveSession': { schema: workspaceArchiveSessionRequestSchema, invoke: (api, r) => api.workspace.archiveSession(r) },
   'command.list': { schema: commandListRequestSchema, invoke: (api, r) => api.commands.list(r) },
   'command.execute': { schema: commandExecuteRequestSchema, invoke: (api, r, signal) => api.commands.execute(r, signal) },
   'skill.list': { schema: skillListRequestSchema, invoke: (api, r) => api.skills.list(r) },