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>

distro-packages/Arch-Linux/cthulhu-git/PKGBUILD

@@ -84,6 +84,7 @@ build() {
 
   go build -o build/cthulhu ./cmd/cthulhu
   go build -tags brlapi -o build/cthulhu-braille ./cmd/cthulhu-braille
+  go build -o build/cthulhu-input-helper ./cmd/cthulhu-input-helper
 }
 
 check() {
@@ -98,6 +99,7 @@ package() {
   cd "${_pkgname}"
   install -Dm755 build/cthulhu "${pkgdir}/usr/bin/cthulhu"
   install -Dm755 build/cthulhu-braille "${pkgdir}/usr/bin/cthulhu-braille"
+  install -Dm755 build/cthulhu-input-helper "${pkgdir}/usr/bin/cthulhu-input-helper"
   install -Dm644 LICENSE "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE"
   install -Dm644 AUTHORS "${pkgdir}/usr/share/doc/${pkgname}/AUTHORS"
 }