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);
+}

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

@@ -7,16 +7,24 @@ import {
   getSessionCredentials,
   getSessionStatus,
 } from "@/modules/parcel-sync/services/session-store";
+import { getEterraHealth } from "@/modules/parcel-sync/services/eterra-health";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
 /**
- * GET /api/eterra/session — returns current server-side session status.
- * Any client can call this to check if eTerra is connected.
+ * GET /api/eterra/session — returns current server-side session status
+ * enriched with eTerra platform health info.
  */
 export async function GET() {
-  return NextResponse.json(getSessionStatus());
+  const status = getSessionStatus();
+  const health = getEterraHealth();
+  return NextResponse.json({
+    ...status,
+    eterraAvailable: health.available,
+    eterraMaintenance: health.maintenance,
+    eterraHealthMessage: health.message,
+  });
 }
 
 /**
@@ -70,6 +78,19 @@ export async function POST(req: Request) {
       );
     }
 
+    // Block login when eTerra is in maintenance
+    const health = getEterraHealth();
+    if (!health.available && health.maintenance) {
+      return NextResponse.json(
+        {
+          error:
+            "eTerra este în mentenanță — conectarea este dezactivată temporar",
+          maintenance: true,
+        },
+        { status: 503 },
+      );
+    }
+
     // Check if already connected with same credentials
     const existing = getSessionCredentials();
     if (existing && existing.username === username) {