refactor(install): generate the web sudoers rules in one place

/etc/sudoers.d/ledmatrix_web was written by two copies of the same
allow-list: a heredoc in first_time_install.sh Step 10 and a block of
echo lines in scripts/install/configure_web_sudo.sh. They drifted before
(safe_pip_install.sh was granted by one only), and a test existed just
to catch that.

Both now call web_sudoers_rules() from the new
scripts/install/lib_sudoers.sh and keep their own validate (visudo -c),
install and confirm flows.

- first_time_install.sh output is byte-for-byte unchanged, so a device
  re-running the installer gets "already up to date". If the library is
  missing, Step 10 keeps the installed file and carries on, the same way
  it handles rules that fail visudo (an empty file would pass visudo).
- configure_web_sudo.sh now writes the installer's layout: same 18 rules,
  different comments and order. It still leaves out reboot, poweroff and
  journalctl when they are missing; the library does that for both.

The drift test now pins the generator's grants, checks that neither
installer writes rules of its own, and runs each installer's call line
to check the argument order. Tests that read the rule text now read the
library.

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

first_time_install.sh

@@ -1516,51 +1516,31 @@ POWEROFF_PATH=$(which poweroff)
 BASH_PATH=$(which bash)
 JOURNALCTL_PATH=$(which journalctl 2>/dev/null || true)
 
-# Create sudoers content
-cat > "$SUDOERS_TMP" << EOF
-# LED Matrix Web Interface passwordless sudo configuration
-# This allows the web interface user to run specific commands without a password
-
-# Allow $ACTUAL_USER to run specific commands without a password for the LED Matrix web interface
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $REBOOT_PATH
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $POWEROFF_PATH
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH start ledmatrix.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH stop ledmatrix.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH restart ledmatrix.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH enable ledmatrix.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH disable ledmatrix.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH status ledmatrix.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH is-active ledmatrix
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH is-active ledmatrix.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH start ledmatrix-web.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH stop ledmatrix-web.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH restart ledmatrix-web.service
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $BASH_PATH $PROJECT_ROOT_DIR/scripts/fix_perms/safe_plugin_rm.sh *
-# Install a requirements.txt as root via vetted helper, so packages are visible
-# to root-run ledmatrix.service (not just the web interface's own user).
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $BASH_PATH $PROJECT_ROOT_DIR/scripts/fix_perms/safe_pip_install.sh *
-EOF
-if [ -n "$JOURNALCTL_PATH" ]; then
-    cat >> "$SUDOERS_TMP" << EOF
-# NOEXEC, because these rules end in a wildcard and journalctl starts a pager
-# when its output is a terminal. From that pager (less) a "!sh" is a root
-# shell -- the standard journalctl escalation. The web interface always passes
-# --no-pager, so nothing here needs it, but the rule cannot require a flag that
-# sits in the middle of the command line. NOEXEC stops the command executing
-# another program at all, which closes the hole without depending on wildcard
-# matching subtleties.
-$ACTUAL_USER ALL=(ALL) NOPASSWD:NOEXEC: $JOURNALCTL_PATH -u ledmatrix.service *
-$ACTUAL_USER ALL=(ALL) NOPASSWD:NOEXEC: $JOURNALCTL_PATH -u ledmatrix *
-$ACTUAL_USER ALL=(ALL) NOPASSWD:NOEXEC: $JOURNALCTL_PATH -t ledmatrix *
-EOF
+# The rules themselves live in scripts/install/lib_sudoers.sh, shared with
+# scripts/install/configure_web_sudo.sh so the two cannot drift apart again.
+# If it is missing (a damaged checkout), keep whatever is already installed
+# rather than failing the whole install; the gate below skips the install.
+SUDOERS_VALID=1
+SUDOERS_LIB="$PROJECT_ROOT_DIR/scripts/install/lib_sudoers.sh"
+if [ -f "$SUDOERS_LIB" ]; then
+    # shellcheck source=scripts/install/lib_sudoers.sh
+    . "$SUDOERS_LIB"
+    web_sudoers_rules "$ACTUAL_USER" "$PROJECT_ROOT_DIR" "$SYSTEMCTL_PATH" "$BASH_PATH" \
+        "$REBOOT_PATH" "$POWEROFF_PATH" "$JOURNALCTL_PATH" > "$SUDOERS_TMP"
+else
+    SUDOERS_VALID=0
+    echo "⚠ $SUDOERS_LIB not found; cannot generate the sudoers rules." >&2
+    echo "⚠ Leaving $SUDOERS_FILE unchanged. The web interface cannot control" >&2
+    echo "  the display service until this is fixed." >&2
 fi
 
 # Never install rules we have not parsed. A malformed drop-in in
 # /etc/sudoers.d makes sudo refuse every command for every user, which on a
 # headless Pi leaves no way in at all. If the rules do not parse, say so and
 # keep whatever is already installed.
-SUDOERS_VALID=1
-if command -v visudo >/dev/null 2>&1; then
+if [ "$SUDOERS_VALID" = "0" ]; then
+    :  # nothing was generated; already reported above
+elif command -v visudo >/dev/null 2>&1; then
     if ! visudo -c -f "$SUDOERS_TMP" >/dev/null 2>&1; then
         SUDOERS_VALID=0
         echo "⚠ The generated sudoers rules did not parse:" >&2