fix: bash 3.2 compat — sed for pattern sub + split local var=$(cmd) (#1572, #1571) (#1587)

Issue #1572: Replace bash 4+ ${//} pattern substitution in generate_env_config
with sed for macOS bash 3.2 compatibility.

Issue #1571: Split local var=$(cmd) declarations in fly/lib/common.sh so
exit codes propagate correctly with set -e on macOS bash 3.2.

Agent: code-health

Co-authored-by: B <6723574+louisgv@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

fly/lib/common.sh

@@ -685,8 +685,10 @@ except Exception:
 
 # List all Fly.io apps and machines
 list_servers() {
-    local org=$(get_fly_org)
-    local response=$(fly_api GET "/apps?org_slug=$org")
+    local org
+    org=$(get_fly_org)
+    local response
+    response=$(fly_api GET "/apps?org_slug=$org")
 
     printf '%s' "$response" | python3 -c "
 import json, sys

shared/common.sh

@@ -1278,7 +1278,9 @@ generate_env_config() {
         fi
 
         # Escape any single quotes in the value: replace ' with '\''
-        local escaped_value="${value//\'/\'\\\'\'}"
+        # Use sed instead of ${//} pattern substitution for bash 3.2 (macOS) compat
+        local escaped_value
+        escaped_value=$(printf '%s' "$value" | sed "s/'/'\\\\''/g")
         echo "export ${key}='${escaped_value}'"
     done
 }