fix(build): include gsd-read-injection-scanner in hooks/dist (#2406)

The scanner was added in #2201 but never added to the HOOKS_TO_COPY
allowlist in scripts/build-hooks.js, so it never landed in hooks/dist/.
install.js reads from hooks/dist/, so every install on 1.37.0/1.37.1
emitted "Skipped read injection scanner hook — not found at target"
and the read-time prompt-injection scanner was silently disabled.

- Add gsd-read-injection-scanner.js to HOOKS_TO_COPY
- Add it to EXPECTED_ALL_HOOKS regression test in install-hooks-copy

Fixes #2406

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/build-hooks.js

@@ -20,6 +20,7 @@ const HOOKS_TO_COPY = [
   'gsd-context-monitor.js',
   'gsd-prompt-guard.js',
   'gsd-read-guard.js',
+  'gsd-read-injection-scanner.js',
   'gsd-statusline.js',
   'gsd-workflow-guard.js',
   // Community hooks (bash, opt-in via .planning/config.json hooks.community)