Replace the Express service with a Next.js app on Vercel

The standalone service in server/ was never deployed anywhere, and keeping it
alongside a Vercel app would mean maintaining two implementations of the same
validation rules. It is deleted; web/ is the only ingest path now. Its routes
live at /v1/... rather than under /api, so the Android client's URL building is
unchanged and CONSUMPTION_API_URL stays a bare origin.

Credentials are split in two. INGEST_TOKEN is baked into the published APK and
must be assumed extractable — anyone can unzip an APK and read its strings — so
it opens the PUT endpoints and nothing else. Reading the history needs the
dashboard password, which is never compiled into anything and reaches the
browser as an HMAC-signed httpOnly cookie. The MongoDB URI stays a server-side
environment variable; the car has never held one and still does not.

The dashboard is a phone-shaped reader for the same data: totals for energy
taken and paid, a daily energy chart, an efficiency trend, and every DC session
with its power/SOC curve. It reuses the head unit's OLED palette so the two read
as one app. Every page is a server component and the charts are hand-rolled SVG,
so the whole thing renders without shipping client JavaScript.

MongoClient is cached on globalThis: a fresh client per request means a fresh
pool per request, and Atlas starts refusing connections long before the traffic
would justify it. Index creation moved to the first write of each warm lambda,
since a serverless deployment has no boot step to hang it on.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/.env.example

@@ -0,0 +1,14 @@
+# MongoDB Atlas connection string. Never leaves the server.
+MONGODB_URI=mongodb+srv://user:password@cluster.mongodb.net/?retryWrites=true&w=majority
+MONGODB_DATABASE=fatihsmg4
+
+# Write-only token the car sends as `Authorization: Bearer ...` on the PUT endpoints.
+# Generate with: openssl rand -hex 32
+INGEST_TOKEN=
+
+# Password for the web dashboard. Anyone who knows it can read the history.
+DASHBOARD_PASSWORD=
+
+# Signs the session cookie. Rotating it logs every browser out.
+# Generate with: openssl rand -hex 32
+SESSION_SECRET=