Restructure Web App into server/ + web/ (GsmNode parity)

Reorganize the Web App to match the GsmNode project layout: a Go
backend-for-frontend in server/ that embeds the built SPA and reverse-proxies
/api/* to the API Server, with the Vue 3 + Vite frontend moved into web/.

- Move all frontend files into web/ (history preserved via renames)
- Point vite build output at ../server/dist for Go embedding
- Add server/ Go BFF (main.go, go.mod, .env.example, Run-WebApp.ps1)
- Drop Docker/nginx deploy (Dockerfile, docker-compose.yml, nginx.conf.template,
  .dockerignore) in favor of the BFF, matching GsmNode
- Update .claude/launch.json to run the dev server from web/
- Rewrite README.md for the new layout

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Web App/web/src/lib/format.js

@@ -0,0 +1,94 @@
+// Formatting + maintenance-status helpers. The status logic follows the
+// spreadsheet idea: a service is "due" when its computed next-service date
+// (service date + interval) approaches/passes today, OR when the car's current
+// odometer approaches/passes the computed next-service km.
+
+import { prefs } from "../prefs.js";
+
+export function formatDate(value) {
+  if (!value) return "—";
+  const d = new Date(value);
+  if (isNaN(d)) return "—";
+
+  const day = String(d.getDate()).padStart(2, "0");
+  const month = String(d.getMonth() + 1).padStart(2, "0");
+  const monthName = d.toLocaleDateString(prefs.locale || undefined, { month: "short" });
+  const year = d.getFullYear();
+
+  switch (prefs.dateFormat) {
+    case "DMY_NUM":
+      return `${day}-${month}-${year}`;
+    case "DMY":
+      return `${day} ${monthName} ${year}`;
+    case "MDY":
+      return `${monthName} ${day}, ${year}`;
+    case "YMD":
+    default:
+      return `${year}-${month}-${day}`;
+  }
+}
+
+export function formatKm(value) {
+  if (value == null || value === "" || value === 0) return "—";
+  return Number(value).toLocaleString() + " km";
+}
+
+const DAY = 24 * 60 * 60 * 1000;
+const KM_SOON = 1000; // within 1000 km of due => "soon"
+
+// daysUntil returns whole days from today to the given date (negative = past).
+export function daysUntil(value) {
+  if (!value) return null;
+  const target = new Date(value);
+  if (isNaN(target)) return null;
+  const today = new Date();
+  today.setHours(0, 0, 0, 0);
+  target.setHours(0, 0, 0, 0);
+  return Math.round((target - today) / DAY);
+}
+
+// Severity ranking so we can pick the worst of the date/km signals.
+const RANK = { unknown: 0, ok: 1, soon: 2, overdue: 3 };
+// DriverVault status language: On track (green) / Due soon (amber) / Action
+// needed (red). Uses the shared badge recipes from style.css so tints flip in
+// dark mode automatically.
+const STYLE = {
+  unknown: "dh-badge dh-badge-neutral",
+  ok: "dh-badge dh-badge-success",
+  soon: "dh-badge dh-badge-warning",
+  overdue: "dh-badge dh-badge-danger",
+};
+
+// dateSignal classifies the next-due date relative to today.
+function dateSignal(nextServiceDate) {
+  const days = daysUntil(nextServiceDate);
+  if (days == null) return { key: "unknown", label: "No data" };
+  if (days < 0) return { key: "overdue", label: `Service Overdue ${Math.abs(days)}d` };
+  if (days <= 30) return { key: "soon", label: `Due in ${days}d` };
+  return { key: "ok", label: `OK · ${days}d` };
+}
+
+// kmSignal classifies the current odometer against the next-due km.
+function kmSignal(currentKm, nextServiceKm) {
+  if (!currentKm || !nextServiceKm) return { key: "unknown", label: "No km" };
+  const remaining = nextServiceKm - currentKm;
+  if (remaining < 0) return { key: "overdue", label: `Service Overdue ${Math.abs(remaining).toLocaleString()} km` };
+  if (remaining <= KM_SOON) return { key: "soon", label: `In ${remaining.toLocaleString()} km` };
+  return { key: "ok", label: `${remaining.toLocaleString()} km left` };
+}
+
+// serviceStatus combines the date- and km-based signals, returning the worse of
+// the two for the badge. `latest` is the most recent service record (with
+// nextServiceDate/nextServiceKm); `car` carries the current odometer.
+export function serviceStatus(latest, car = null) {
+  const date = dateSignal(latest?.nextServiceDate);
+  const km = kmSignal(car?.currentKm, latest?.nextServiceKm);
+
+  const worse = RANK[km.key] > RANK[date.key] ? km : date;
+  // If only one signal has data, use that one's label.
+  let label = worse.label;
+  if (date.key === "unknown" && km.key !== "unknown") label = km.label;
+  else if (km.key === "unknown" && date.key !== "unknown") label = date.label;
+
+  return { key: worse.key, label, classes: STYLE[worse.key], date, km };
+}