feat(parcel-sync): eTerra health check + maintenance detection

- New eterra-health.ts service: pings eTerra periodically (3min),
  detects maintenance (503, keywords), tracks consecutive failures
- New /api/eterra/health endpoint for explicit health queries
- Session route blocks login when eTerra is in maintenance (503 response)
- GET /api/eterra/session now includes eterraAvailable/eterraMaintenance
- ConnectionPill shows amber 'Mentenanță' state with AlertTriangle icon
  instead of confusing red error when eTerra is down
- Auto-connect skips when maintenance detected, retries when back online
- 30s session poll auto-detects recovery and re-enables auto-connect

src/app/api/eterra/health/route.ts

@@ -0,0 +1,27 @@
+/**
+ * GET /api/eterra/health — eTerra platform availability check.
+ *
+ * Returns health status without requiring authentication.
+ * Triggers a fresh check if cached result is stale.
+ *
+ * POST /api/eterra/health — force an immediate fresh check.
+ */
+
+import { NextResponse } from "next/server";
+import {
+  getEterraHealth,
+  checkEterraHealthNow,
+} from "@/modules/parcel-sync/services/eterra-health";
+
+export const runtime = "nodejs";
+export const dynamic = "force-dynamic";
+
+export async function GET() {
+  const health = getEterraHealth();
+  return NextResponse.json(health);
+}
+
+export async function POST() {
+  const health = await checkEterraHealthNow();
+  return NextResponse.json(health);
+}