feat(web): Start Display on Boot toggle on the General tab

Turns ledmatrix.service's autostart on or off at once through the existing
enable_autostart / disable_autostart system actions (sudo grants already in
lib_sudoers.sh). The checkbox shows systemd's own state, read with
`systemctl is-enabled`, so nothing is stored in config.json and the default
stays on. Hidden when the state cannot be read; a refused change puts the
box back and shows the route's message.

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

test/js/run_all.js

@@ -32,7 +32,8 @@ const UNIT = ['unit/test_list_filter.js', 'unit/test_render_cards.js',
               'unit/test_page_registry.js', 'unit/test_core_modules.js',
               'unit/test_overview_reconciliation_poll.js',
               'unit/test_display_partial_ids.js',
-              'unit/test_general_web_login_token.js'];
+              'unit/test_general_web_login_token.js',
+              'unit/test_general_display_autostart.js'];
 const DOM = ['dom/test_installed_dom.js', 'dom/test_store_dom.js', 'dom/test_no_double_fetch.js',
              'dom/test_tools_sections.js', 'dom/test_cache_page.js',
              'dom/test_durations_page.js', 'dom/test_operation_history_page.js',