feat(parcel-sync): sync-to-DB + local export + layer catalog enhancements

Layer catalog now has 3 actions per layer:
- Sync: downloads from eTerra, stores in PostgreSQL (GisFeature table),
  incremental — only new OBJECTIDs fetched, removed ones deleted
- GPKG: direct download from eTerra (existing behavior)
- Local export: generates GPKG from local DB (no eTerra needed)

New features:
- /api/eterra/export-local endpoint — builds GPKG from DB, ZIP for multi-layer
- /api/eterra/sync now uses session-based auth (no credentials in request)
- Category headers show both remote + local feature counts
- Each layer shows local DB count (violet badge) + last sync timestamp
- 'Export local' button in action bar when any layer has local data
- Sync progress message with auto-dismiss

DB schema already had GisFeature + GisSyncRun tables from prior work.

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

@@ -1,5 +1,6 @@
 import { NextResponse } from "next/server";
 import { syncLayer } from "@/modules/parcel-sync/services/sync-service";
+import { getSessionCredentials } from "@/modules/parcel-sync/services/session-store";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
@@ -18,15 +19,12 @@ type Body = {
 export async function POST(req: Request) {
   try {
     const body = (await req.json()) as Body;
-    const username = (
-      body.username ??
-      process.env.ETERRA_USERNAME ??
-      ""
+    const session = getSessionCredentials();
+    const username = String(
+      body.username || session?.username || process.env.ETERRA_USERNAME || "",
     ).trim();
-    const password = (
-      body.password ??
-      process.env.ETERRA_PASSWORD ??
-      ""
+    const password = String(
+      body.password || session?.password || process.env.ETERRA_PASSWORD || "",
     ).trim();
     const siruta = String(body.siruta ?? "").trim();
     const layerId = String(body.layerId ?? "TERENURI_ACTIVE").trim();