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]>

docs/typescript_port_compatibility_matrix.md

@@ -50,7 +50,7 @@ until a later milestone.
 
 | Environment | Status |
 |---|---|
-| Node 22 (vitest) | green — 151/151 core + 41 CLI |
+| Node 22 (vitest) | green — 151/151 core + 44 CLI |
 | jsdom browser-like env | green — 148/148 core (3 transport tests Node-only) |
 | Real Chromium/Firefox (vitest browser mode) | todo — lands with Milestone 6 web app CI |