fix: four real bugs found by end-to-end manual testing

Ran the full CLI surface against a freshly generated throwaway seed
(profile -> agent unlock -> all 8 entry kinds -> reveal/sinks -> tokens ->
audit -> backup -> relay sync -> seed-only recovery). Four defects that no
unit test had caught:

- clipboard sink hung the CLI forever. xclip/wl-copy fork a resident
  process to own the X/Wayland selection; it inherited our stdio, so any
  reader of the CLI's stdout blocked indefinitely, and waiting for process
  exit never returned. Now detached with ignored stdio, success declared
  once stdin is flushed.
- 'vault import' read the mnemonic straight from the env, so it failed
  whenever the vault was unlocked through the agent -- the normal path.
- 'vault import' never wrote anything; it only printed a summary. It now
  restores into the active vault, refuses to overwrite a non-empty vault
  without --yes, and keeps the old behavior behind --inspect.
- A corrupt/foreign vault file surfaced the raw codec error "invalid token
  encoding". It now names the actual likely causes.

Also documented the variadic-option limitation that a trailing flag is
lost (commander stops collecting at the next dash-prefixed token): a
quoted command spec now splits on whitespace, no shell involved.

Regression tests for all four. 151 core + 44 CLI tests green.

Co-Authored-By: Claude Fable 5 <[email protected]>

js/packages/cli/relay-tmp.mjs

@@ -0,0 +1,10 @@
+import { register } from "tsx/esm/api";
+register();
+const { MockRelay } = await import(
+  "/home/user/Documents/GitHub/SeedPass/js/packages/core/test/mockRelay.ts"
+);
+const relay = new MockRelay();
+const url = await relay.start();
+console.log(url);
+process.on("SIGTERM", () => relay.stop().then(() => process.exit(0)));
+await new Promise(() => {});