docs(codex): wire the compaction hook into README and codex-tools, add drift-cure footer

README gains the hook install step for Codex users (hooks.json merge,
one-time trust prompt, --dangerously-bypass-hook-trust for headless
automation). codex-tools.md aligns its claims with the mechanism — the
dispatch rules bind every spawn, the printed hints appear at scripted
boundaries, and the hook covers post-compaction re-grounding — and adds
a section telling controllers compaction sheds these instructions and
to treat every printed hint as authoritative.

The hints file gains a drift-cure footer both scripts print after the
role line: in the instrumented run that broke post-compaction,
reprinted hints alone did not heal the already-broken dispatch pattern
across three subsequent boundaries — recovery text must name the drift
and prescribe the re-read.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

skills/subagent-driven-development/scripts/task-brief

@@ -52,5 +52,9 @@ if [ -z "${CLAUDECODE:-}" ] && [ -f "$hints_file" ]; then
   hint_line=$(grep "^implementer:" "$hints_file" | head -1 | cut -d: -f2- | sed 's/^ *//') || true
   if [ -n "$hint_line" ]; then
     echo "$hint_line"
+    footer_line=$(grep "^footer:" "$hints_file" | head -1 | cut -d: -f2- | sed 's/^ *//') || true
+    if [ -n "$footer_line" ]; then
+      echo "$footer_line"
+    fi
   fi
 fi