fix(update.sh): stop config sync loop from dying silently on a missing key

current=$(grep ...) ran before checking whether the key existed in .env
at all. Under set -euo pipefail, a key missing from .env (e.g. a new
tunable this branch just added to .env.example) made that grep exit 1,
pipefail propagated it, and set -e killed the script instantly with no
output - looked exactly like a gum hang but never reached ensure_gum.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bs8xf8Dt8X6tRBvBiLCXYc

scripts/update.sh

@@ -93,10 +93,12 @@ conflict_old=()
 conflict_new=()
 while IFS='=' read -r key value; do
   [ -n "$value" ] || continue
-  current="$(grep -E "^${key}=" .env | head -1 | cut -d= -f2-)"
   if ! grep -qE "^${key}=" .env; then
     echo "${key}=${value}" >> .env
-  elif [ "$current" != "$value" ]; then
+    continue
+  fi
+  current="$(grep -E "^${key}=" .env | head -1 | cut -d= -f2-)"
+  if [ "$current" != "$value" ]; then
     conflict_keys+=("$key")
     conflict_old+=("$current")
     conflict_new+=("$value")