fix(remote): authorize the attach wake first; tell the caller what happened to its bytes

Review round 3 on #439.

- The attachRemoteSession branch of POST /api/sessions ran `ensureHostAwake`
  before the multi-user gates, so a non-admin could have any configured
  host's `wakeCommand` spawned (or a packet broadcast) and the request held
  for the wake budget, then be refused for the workingDir. The admin gate
  now comes first, before the host is even looked up; remote hosts are
  admin-only infrastructure everywhere else. Route test: wake spy empty,
  403.
- The non-wait input route answers `{buffered:true}` when the registry took
  the chunk and `{buffered:true, dropped:true}` when it was over the cap
  and is gone (`RemoteInputOutcome` gains 'dropped'); additive to the bare
  `{}`.
- The send-and-wait path answers OPERATION_FAILED when the host never comes
  back, like create and attach, instead of writing into the stalled pane
  and reporting delivered:true plus a timeout.
- The flush writes with `fromUser: true`, so a first prompt buffered
  through a wake can still name the tab.

Docs: api-reference (input route), remote-sessions.md (two invariants),
CLAUDE.md key pattern.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QdGP4jUTjc9J2RYYykDrCG

docs/api-reference.md

@@ -324,6 +324,16 @@ from the session's current state rather than requiring a new transition: the
 original turn may be long over. It comes back as
 `"delivered": false, "duplicate": true`.
 
+**Wake-on-LAN hosts** (`docs/remote-sessions.md` §Wake-on-LAN): when the session's
+remote host has a wake target and is asleep, the non-wait form answers `200` with
+`{"buffered": true}` — the bytes are held and flushed after the host is back — or
+`{"buffered": true, "dropped": true}` for a chunk over the 4 KB wake buffer, which
+is gone (never delivered as a fragment). Both fields are additive to the historical
+bare `{}`. With `wait`, the route blocks on the wake instead and answers
+`422 OPERATION_FAILED` ("did not come back after a wake-on-LAN request — nothing was
+sent") when the host never returns, rather than writing into the stalled pane and
+reporting `delivered:true` plus a timeout.
+
 ### Response
 
 All three nest the wait result under `data.wait`, so one client helper works against