Minor cleanups: default TZ to UTC, shellcheck directive, comment clarity (#21)

- Default timezone to UTC instead of America/New_York
- Add shellcheck shell=bash directive to .zshrc
- Extract docker filter label into local variable in cmd_down
- Clarify mount filter comment (target paths immune to project name changes)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.zshrc

@@ -1,3 +1,4 @@
+# shellcheck shell=bash
 # Zsh configuration for Claude Code devcontainer
 
 # Add Claude Code to PATH

devcontainer.json

@@ -4,7 +4,7 @@
   "build": {
     "dockerfile": "Dockerfile",
     "args": {
-      "TZ": "${localEnv:TZ:America/New_York}",
+      "TZ": "${localEnv:TZ:UTC}",
       "GIT_DELTA_VERSION": "0.18.2",
       "ZSH_IN_DOCKER_VERSION": "1.2.1"
     }

install.sh

@@ -109,7 +109,7 @@ extract_mounts_to_file() {
 
   temp_file=$(mktemp)
 
-  # Filter out default mounts (template mounts we don't want to preserve)
+  # Filter out default mounts by target path (immune to project name changes)
   local custom_mounts
   custom_mounts=$(jq -c '
     .mounts // [] | map(
@@ -248,8 +248,9 @@ cmd_down() {
   log_info "Stopping devcontainer..."
 
   # Get container ID and stop it
+  local label="devcontainer.local_folder=$workspace_folder"
   local container_id
-  container_id=$(docker ps -q --filter "label=devcontainer.local_folder=$workspace_folder" 2>/dev/null || true)
+  container_id=$(docker ps -q --filter "label=$label" 2>/dev/null || true)
 
   if [[ -n "$container_id" ]]; then
     docker stop "$container_id"