ui: drop the network-monitor area line, label the refresh time (v2.7.5)

The second line under the location (e.g. "RAI FFFE") showed only the LAC
part of the current area identity: after every dummy-writing scenario it
was the constant FFFE, and otherwise it was redundant with the
EF.LOCI/PSLOCI/EPSLOCI rows below.  netStateRender no longer renders it.

The timestamp line now carries a translated "Last refresh" label
('Last refresh': 'Последнее обновление').

- frontend/index.html: remove #netstate-area (markup + render), label the
  read time, LANG_RU entry
- frontend/tests: html test pins the label and the absence of the area
  line; netstate test asserts the rendered timestamp
- sw.js cache simple-v208; version trio 2.7.5

frontend/tests/html.test.js

@@ -293,3 +293,8 @@ test('SCP81 listener exposes its four modes with the matching notes', () => {
     assert.ok(html.includes("mode === 'redirect' && (!hostVal || !portVal)"));
     assert.ok(html.includes("el.disabled = (mode === 'passthru')"));
 });
+
+test('the network monitor labels its refresh timestamp and has no area line', () => {
+    assert.match(html, /data-l10n="Last refresh">Last refresh<\/span>: <span id="netstate-read"><\/span>/);
+    assert.ok(!/id="netstate-area"/.test(html), 'the area line is gone; LAI/RAI/TAI live in the EF rows');
+});