Fix installation directory handling and clarify defaults

- Fixed bootstrap-installer to prompt for installation directory with /opt/trans-install as default
- Updated main-installer to detect and use existing installation path from service file
- Modified config-module to use installation directory from environment or default to /opt/trans-install
- Updated README with clear information about the default installation path
- Bumped version to 2.0.7

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

modules/config-module.sh

@@ -2,7 +2,7 @@
 # Configuration module for Transmission RSS Manager Installation
 
 # Configuration variables with defaults
-INSTALL_DIR="/opt/transmission-rss-manager"
+INSTALL_DIR=${INSTALL_DIR:-"/opt/trans-install"}
 CONFIG_DIR="/etc/transmission-rss-manager"
 SERVICE_NAME="transmission-rss-manager"
 PORT=3000