feat(permission): permissions projection unit and /permission command

The read side becomes the 'permissions' session projection: src/types.ts is
the key declaration's one home (PermissionSelect = whole select: table
options in declaration order plus a current-only 'custom'), served through
./types and the ./client re-export. The unit folds the three whole-value
knob events (permission/preset, sandbox/mode, approval/policy) into a plain
KnobState and views the select over the composition defaults the service
already owns; current() shares the same derive step, so the fold exists
once. The write side becomes the /permission command (the /plan
registration shape): bare invocation reports the current preset and the
table, a preset argument switches through set() immediately — no turn
anchoring (knob events need no enclosure), no dedicated RPC. Both children
activate only when their registry is composed.

packages/ui/permission/src/client.ts

@@ -0,0 +1,10 @@
+/**
+ * Client-namespace projection of the permission domain: a pure re-export of
+ * the package's types outlet. Client code imports ONLY the client namespace
+ * (repo discipline), so `./client` projects the same single-source content
+ * `./types` serves to host consumers — zero duplication.
+ *
+ * @module @deepseek-ai/dsh-permission/client
+ */
+
+export type * from './types.ts'