refactor(cockpit): share one header frame between the Cockpit cards

The Contact and briefing cards' headers repeated the same frame: the title
grid over a hairline, the accent kicker and the square action buttons. It
lives in cockpit-card-header, cockpit-card-kicker and cockpit-card-actions
now, beside each card's own classes, which keep only their spacing and
sizes; the cyber theme targets the shared classes. The computed styles of
every header element are unchanged in the default and cyber themes,
expanded and collapsed.

src/cockpitMarkup.test.mjs

@@ -1188,7 +1188,7 @@ test('cockpit summary presents the focused item as Contact', () => {
   const match = html.match(/<aside id="cockpit-context"[\s\S]*?<\/aside>/);
   assert.ok(match, 'cockpit Contact summary is missing');
   assert.match(match[0], /aria-label="Contact cockpit summary"/);
-  assert.match(match[0], /class="cockpit-context-kicker">CONTACT</);
+  assert.match(match[0], /class="cockpit-card-kicker cockpit-context-kicker">CONTACT</);
   assert.match(match[0], /aria-label="Contact navigation"/);
   assert.match(
     match[0],