s04_hooks: permission_hook checks path + asks user, but safe_path
still raised hard ValueError — user approval was ineffective, same
root cause as s03 (#482).
s20_comprehensive: permission_hook used safe_path directly inside
try/except, silently denying all writes outside workspace without
ever asking the user. Now uses is_relative_to check + user prompt.
Both files also add read_file to the permission coverage.
s05-s08 intentionally NOT changed: their permission_hook does not
check paths at all — safe_path is their only path-safety defense.
The problem block used a nested `if block.type == "tool_use":` while the
solution block and code.py use `if block.type != "tool_use": continue`.
This made the problem->solution diff show two changes instead of the one
the section teaches (the README states only one place in the loop changed).
Align all three README variants (zh/en/ja) to the early-continue idiom.
