Added scripts to install HACS in DevContainer for testing the
integration alongside other HACS components.
Changes:
- scripts/setup: Automatically install HACS and create symlink
- scripts/sync-hacs: Sync HACS-installed integrations via symlinks
- .gitignore: Ignore custom_components/* except tibber_prices
HACS installs to config/custom_components/, symlinks in
custom_components/ make integrations visible to Home Assistant.
Impact: Developers can test with other integrations. No user changes.
