Card bulk operations, remove expand/collapse, graph color picker fix

- Bulk selection mode: Ctrl+Click or toggle button to enter, Escape to exit
- Shift+Click for range select, bottom toolbar with SVG icon action buttons
- All CardSections wired with bulk actions: Delete everywhere,
  Start/Stop for targets, Enable/Disable for automations
- Remove expand/collapse all buttons (no collapsible sections remain)
- Fix graph node color picker overlay persisting after outside click
- Add Icons section to frontend.md conventions
- Add trash2, listChecks, circleOff icons to icon system
- Backend: processing loop performance improvements (monotonic timestamps,
  deque-based FPS tracking)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

contexts/frontend.md

@@ -151,6 +151,24 @@ The app has an interactive tutorial system (`static/js/features/tutorials.js`) w
 
 When adding **new tabs, sections, or major UI elements**, update the corresponding tutorial step array in `tutorials.js` and add `tour.*` i18n keys to all 3 locale files (`en.json`, `ru.json`, `zh.json`).
 
+## Icons
+
+**Always use SVG icons from the icon system, never text/emoji/Unicode symbols for buttons and UI controls.**
+
+- Icon SVG paths are defined in `static/js/core/icon-paths.js` (Lucide icons, 24×24 viewBox)
+- Icon constants are exported from `static/js/core/icons.js` (e.g. `ICON_START`, `ICON_TRASH`, `ICON_EDIT`)
+- Use `_svg(path)` wrapper from `icons.js` to create new icon constants from paths
+
+When you need a new icon:
+1. Find the Lucide icon at https://lucide.dev
+2. Copy the inner SVG elements (paths, circles, rects) into `icon-paths.js` as a new export
+3. Add a corresponding `ICON_*` constant in `icons.js` using `_svg(P.myIcon)`
+4. Import and use the constant in your feature module
+
+Common icons: `ICON_START` (play), `ICON_STOP` (power), `ICON_EDIT` (pencil), `ICON_CLONE` (copy), `ICON_TRASH` (trash), `ICON_SETTINGS` (gear), `ICON_TEST` (flask), `ICON_OK` (circle-check), `ICON_WARNING` (triangle-alert), `ICON_HELP` (circle-help), `ICON_LIST_CHECKS` (list-checks), `ICON_CIRCLE_OFF` (circle-off).
+
+For icon-only buttons, use `btn btn-icon` CSS classes. The `.icon` class inside buttons auto-sizes to 16×16.
+
 ## Localization (i18n)
 
 **Every user-facing string must be localized.** Never use hardcoded English strings in `showToast()`, `error.textContent`, modal messages, or any other UI-visible text. Always use `t('key')` from `../core/i18n.js` and add the corresponding key to **all three** locale files (`en.json`, `ru.json`, `zh.json`).