feat: wireview pin-imbalance warning, per-pin rating bars, pin_imbalance_a

- Per-pin bar now scales against the 9.2 A per-pin rating (10 A full
  scale, red at/over rating) instead of the 55 A total connector OCP
- Debounced app-wide warning banner (visible on all tabs) when the
  current between two pins diverges by > 2 A for ~7 s - the signature
  of a bad pin contact that can overheat and melt the 12VHPWR
  connector; 5 s grace period after clearing
- New pin_imbalance_a sample field (max - min pin current) in both the
  serial and hwmon sample builders, plus frontend type
- Docs: README + WireView.md cover the warning and threshold; fresh
  screenshot with the new per-pin labels
- Tests: vitest setup + 9 unit tests for the debounce state machine;
  3 new backend checks for pin_imbalance_a

frontend/package.json

@@ -7,6 +7,7 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "eslint .",
+    "test": "vitest run",
     "preview": "vite preview"
   },
   "dependencies": {
@@ -20,6 +21,7 @@
   "devDependencies": {
     "@eslint/js": "^9.39.1",
     "@tailwindcss/vite": "^4.2.1",
+    "@testing-library/react": "^16.3.3",
     "@types/d3": "^7.4.3",
     "@types/node": "^24.10.1",
     "@types/react": "^19.2.7",
@@ -29,9 +31,11 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.4.24",
     "globals": "^16.5.0",
+    "happy-dom": "^20.14.5",
     "tailwindcss": "^4.2.1",
     "typescript": "~5.9.3",
     "typescript-eslint": "^8.48.0",
-    "vite": "^7.3.1"
+    "vite": "^7.3.1",
+    "vitest": "^5.0.3"
   }
 }