fix: escape sed special chars + reject & | / in passwords

Reviewer found a password like aA1!@#%^&*()_-+={}[] becomes
aA1!@#%^__ADMIN_PW__*()_-+={}[] because sed expands & to matched
pattern. Two layers of defense:
1. validate_pw rejects & | / newline at input
2. sed_escape() helper escapes any remaining special chars before
   substitution

overlay/usr/local/sbin/veilor-installer

@@ -202,17 +202,23 @@ collect_answers() {
     # ── Hostname ──
     hostname=$(prompt_input "Set hostname" "veilor") || return 1
 
-    # Reject shell-special chars in passwords. Generated kickstart writes
-    # them via heredoc + sed substitution; bare $, ", \, ` would corrupt
-    # the ks line or partially expand. 8-char min for entropy.
+    # Reject shell-special and sed-special chars in passwords. Generated
+    # kickstart writes them via heredoc + sed substitution; bare $, ", \, `
+    # would corrupt the ks line or partially expand at heredoc time.
+    # &, |, /, newline are sed-special: & expands to the matched pattern
+    # (so `aA1!@#%^&*()` becomes `aA1!@#%^__ADMIN_PW__*()`), | is our
+    # delimiter, / would match if delimiter changes, newline breaks the
+    # sed expression. sed_escape() below adds defense-in-depth, but we
+    # also reject these at input so the user sees an immediate error
+    # rather than a corrupted ks file. 8-char min for entropy.
     validate_pw() {
         local pw=$1 label=$2
         if [[ ${#pw} -lt 8 ]]; then
             prompt_error "Weak $label — minimum 8 characters."
             return 1
         fi
-        if [[ $pw =~ [\"\$\\\`] ]]; then
-            prompt_error "Invalid $label — cannot contain: \" \$ \\ \`"
+        if [[ $pw =~ [\"\$\\\`\&\|/$'\n'] ]]; then
+            prompt_error "Invalid $label — cannot contain: \" \$ \\ \` & | / newline"
             return 1
         fi
         return 0
@@ -253,6 +259,17 @@ Proceed?" || return 1
     return 0
 }
 
+# sed_escape — escape sed special chars in a replacement string.
+# Replacement-side metacharacters: & (matched pattern), \ (escape),
+# | (our chosen delimiter), / (alternate delimiter — escape too in case
+# delimiter ever changes). Newline is rejected in validate_pw because
+# escaping it portably across BSD/GNU sed is fiddly.
+# Order matters: \ must be escaped FIRST so we don't double-escape the
+# backslashes we're about to emit for &, |, /.
+sed_escape() {
+    printf '%s' "$1" | sed -e 's/[\\&|/]/\\&/g'
+}
+
 generate_ks() {
     # Build kickstart for actual disk install.
     # NOTE: passwords go in via --plaintext to avoid storing crypted hash
@@ -483,15 +500,16 @@ echo "════════════════════════
 # Reboot when done
 reboot
 KSEOF
-    # Substitute placeholders. Use | as sed delimiter (passwords might
-    # contain /). Forbidden chars in passwords (validated upstream): "$\`
-    # — sed safe.
+    # Substitute placeholders. Use | as sed delimiter. validate_pw()
+    # already rejects "$\`&|/\n at input — sed_escape() is defence in
+    # depth in case future code paths feed unsanitised values (e.g.
+    # locale/hostname from a file, or a relaxed validator).
     sed -i \
-        -e "s|__LOCALE__|$SEL_LOCALE|" \
-        -e "s|__HOSTNAME__|$SEL_HOSTNAME|" \
-        -e "s|__DISK_BASENAME__|$disk_basename|" \
-        -e "s|__LUKS_PW__|$SEL_LUKS_PW|" \
-        -e "s|__ADMIN_PW__|$SEL_ADMIN_PW|" \
+        -e "s|__LOCALE__|$(sed_escape "$SEL_LOCALE")|" \
+        -e "s|__HOSTNAME__|$(sed_escape "$SEL_HOSTNAME")|" \
+        -e "s|__DISK_BASENAME__|$(sed_escape "$disk_basename")|" \
+        -e "s|__LUKS_PW__|$(sed_escape "$SEL_LUKS_PW")|" \
+        -e "s|__ADMIN_PW__|$(sed_escape "$SEL_ADMIN_PW")|" \
         "$out"
     echo "[INFO] generated kickstart at $out"
     return 0