Attach Remote keyboard injection to approved controlled sessions

Local launch and managed startup now start the incoming-key owner for
sessions installed with keyboard-inject, using one input-helper
Supervisor retained for the reader lifetime. Delivery rechecks lock,
XTerm handoff and internal reader UI in addition to lease, grant and
deadline. build-cthulhu.sh and both Arch packages build and install
cthulhu-input-helper; a missing helper leaves keyboard input
unavailable without affecting startup.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/remoteinput/supervisor.go

@@ -26,10 +26,10 @@ var (
 const operationTimeout = time.Second
 const retirementTimeout = Watchdog + time.Second
 
-// Supervisor is a quarantined reader-side process owner. It grants no consent
-// and is not attached to the production key mailbox. A future owner must bind
-// ctx/epoch to an approved lease and recheck native policy before every Apply.
-// Unconfirmed cleanup permanently blocks replacement on this Supervisor.
+// Supervisor is the reader-side helper process owner. It grants no consent.
+// Its production owner binds ctx/epoch to an approved lease and rechecks
+// native policy before every Apply. Unconfirmed cleanup permanently blocks
+// replacement on this Supervisor.
 type Supervisor struct {
 	mu        sync.Mutex
 	active    bool