Add robust command availability checks to all shell scripts

- Add check for @defaultPackageName@-devenv in activateDevenv.sh
- Add check for uv command in initPython.sh
- Add check for git command in initProject.sh (with graceful degradation)
- Add checks for wget, sed, nix in updateDeps.sh
- Provide clear error messages when commands are not available
- Prevent scripts from failing with cryptic errors when tools are missing

Co-authored-by: dwinkler1 <22460147+dwinkler1@users.noreply.github.com>

templates/rde/scripts/initPython.sh

@@ -1,5 +1,14 @@
 #!/usr/bin/env bash
 set -euo pipefail
+
+# Check if uv command is available
+if ! command -v uv &> /dev/null; then
+  echo "❌ Command 'uv' not found."
+  echo "UV is required for Python project management."
+  echo "Ensure UV is properly installed in your environment."
+  exit 1
+fi
+
 if [[ ! -f "pyproject.toml" ]]; then
   echo "🐍 Initializing UV project..."
   uv init