chore(scripts): delete unreferenced helper scripts

None of these is referenced by an installer, systemd unit, CI workflow,
test, the web UI or src/:

- utils/cleanup_venv.sh removes venv_web_v2, which nothing creates
- utils/clear_python_cache.sh hardcodes ~/LEDMatrix and a .webassets-cache
  nothing uses
- install/migrate_config.sh only copies the template, which the installer
  and ConfigManager already do
- install/debug_install.sh, debug/debug_web_manual.py
- diagnose_web_ui.sh and verify_web_ui.sh overlap diagnose_web_interface.sh,
  which the docs point to
- fix_internet_connectivity.sh is iptables-only (stale on nftables)
- diagnose_plugin_permissions.sh, dev/validate_python.py
- download_nba_logos.py + README_NBA_LOGOS.md: logo_downloader fetches
  logos on demand
- setup_plugin_repos.py linked into the production plugin-repos/ dir; the
  dev workflow is scripts/dev/dev_plugin_setup.sh, and
  MULTI_ROOT_WORKSPACE_SETUP.md now uses it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/utils/README.md

@@ -7,8 +7,6 @@ This directory contains utility scripts for maintenance and system operations.
 - **`clear_cache.py`** - Clears LEDMatrix cache data (specific keys or all cache)
 - **`start_web_conditionally.py`** - Conditionally starts the web interface based on config settings
 - **`wifi_monitor_daemon.py`** - Background daemon that monitors WiFi/Ethernet connection and manages access point mode
-- **`cleanup_venv.sh`** - Cleans up Python virtual environment files
-- **`clear_python_cache.sh`** - Clears Python cache files (__pycache__, *.pyc, etc.)
 - **`pixlet_config_editor.sh`** - Opens Pixlet's own config UI for one installed Starlark app
 - **`apply_dns_single_request.sh`** - Adds `options single-request` to the resolver (run by `ledmatrix-dns-fix.service`)