feat: extract .env validators to common.sh and add validate_env()

Move 10 validation functions from configure_env.sh to lib/common.sh as
shared utilities. Define variable-to-validator mapping using parallel
arrays (bash 3.2 compatible). validate_env() checks all ~50 .env
variables against their expected format and reports all failures at once.

Wired into preflight.sh (Check 6b) and bitwarden_to_env.sh (post-restore).
configure_env.sh now sources validators from common.sh instead of
defining its own copies.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

setup/configure_env.sh

@@ -11,6 +11,10 @@ PROJECT_ROOT="${SCRIPT_DIR}/.."
 ENV_FILE="${PROJECT_ROOT}/.env"
 ENV_EXAMPLE="${PROJECT_ROOT}/.env.example"
 
+# shellcheck source=../lib/common.sh
+# shellcheck disable=SC1091
+source "${PROJECT_ROOT}/lib/common.sh"
+
 # Colors
 if [[ -t 1 ]]; then
   C_RESET='\033[0m'; C_BOLD='\033[1m'; C_GREEN='\033[0;32m'
@@ -52,47 +56,10 @@ while IFS= read -r line; do
 done < "$ENV_FILE"
 
 # ---------------------------------------------------------------------------
-# Validation functions
+# Validation functions — sourced from lib/common.sh (validate_ip, validate_port,
+# validate_email, validate_path, validate_url, validate_bool, validate_integer,
+# validate_nonempty, validate_password, validate_ssl_mode)
 # ---------------------------------------------------------------------------
-validate_ip() {
-  [[ "$1" =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]]
-}
-
-validate_port() {
-  [[ "$1" =~ ^[0-9]+$ ]] && [[ "$1" -ge 1 ]] && [[ "$1" -le 65535 ]]
-}
-
-validate_email() {
-  [[ "$1" == *@* ]]
-}
-
-validate_path() {
-  [[ "$1" == /* ]]
-}
-
-validate_url() {
-  [[ "$1" =~ ^https?:// ]]
-}
-
-validate_bool() {
-  [[ "$1" == "true" ]] || [[ "$1" == "false" ]]
-}
-
-validate_integer() {
-  [[ "$1" =~ ^[0-9]+$ ]]
-}
-
-validate_nonempty() {
-  [[ -n "$1" ]]
-}
-
-validate_password() {
-  [[ ${#1} -ge 8 ]]
-}
-
-validate_ssl_mode() {
-  [[ "$1" == "letsencrypt" ]] || [[ "$1" == "existing" ]]
-}
 
 # ---------------------------------------------------------------------------
 # Prompt function