[feat](trx-frontend-http): box the selected tab instead of underlining it

The desktop strip marked the current page with a 2px underline while the
mobile bottom nav already boxed it, so one navigation model looked like
two.  The box now sits on both: a transparent 1px border on the base
reserves it, so switching pages moves no neighbours, and hover fills a
fainter version of the same shape.  Tools carries it too — that button
is marked active for the destinations the strip hides.

Dropping the mobile rule's border-bottom:none, which only existed to
cancel the old desktop underline, closes the bottom edge its active box
had been missing.  The smoke test checks all four edges.

Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -1550,19 +1550,34 @@ small { color: var(--text-muted); }
   .tab-bar-nav .tab .tab-icon, .tab-bar-nav .tab .tab-more-icon { display: block; }
   .tab-bar-nav .tab { padding: 0.5rem 0.6rem; }
 }
+/* The selected destination is boxed, not underlined — the same treatment the
+   mobile bottom nav already used, so one navigation model reads the same at
+   every width. The transparent border is on the base so switching tabs moves
+   no neighbours. */
 .tab {
   background: transparent;
-  border: none;
+  border: 1px solid transparent;
-  border-bottom: 2px solid transparent;
+  border-radius: var(--radius-md);
-  border-radius: 0;
+  padding: 0.45rem 0.9rem;
-  padding: 0.5rem 0.95rem;
   color: var(--text-muted);
   cursor: pointer;
   font-size: 0.95rem;
   height: auto;
+  transition: color var(--dur-fast) var(--ease-standard),
+              background-color var(--dur-fast) var(--ease-standard),
+              border-color var(--dur-fast) var(--ease-standard);
+}
+.tab.active {
+  border-color: color-mix(in srgb, var(--accent-green) 50%, var(--border-light));
+  background: color-mix(in srgb, var(--accent-green) 12%, transparent);
+  color: var(--accent-text);
+  font-weight: 600;
+}
+.tab:hover:not(.active) {
+  color: var(--text);
+  background: color-mix(in srgb, var(--btn-bg) 55%, transparent);
+  border-color: color-mix(in srgb, var(--border-light) 40%, transparent);
 }
-.tab.active { border-bottom-color: var(--accent-green); color: var(--accent-text); font-weight: 600; }
-.tab:hover:not(.active) { color: var(--text); }
 /* Tab icons — hidden on desktop, shown on mobile bottom nav */
 .tab-icon {
   display: none;
@@ -3361,7 +3376,6 @@ body[data-operator-layout="broadcast"] #cw-bar-overlay {
     min-height: 3.2rem;
     padding: 0.35rem 0.1rem 0.3rem;
     border: 1px solid transparent;
-    border-bottom: none;
     border-radius: 0.75rem;
     white-space: nowrap;
     text-align: center;

src/trx-client/trx-frontend/trx-frontend-http/frontend/tests/browser-smoke.mjs

@@ -10,7 +10,7 @@ import { fileURLToPath } from "node:url";
 import { chromium } from "playwright-core";
 
 // page.evaluate callbacks run in the browser, not in this Node process.
-/* global document */
+/* global document, getComputedStyle */
 
 const frontendDir = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
 const webDir = path.resolve(frontendDir, "../assets/web");
@@ -213,6 +213,21 @@ try {
   await page.locator("#aprs-map .leaflet-pane").first().waitFor({ state: "attached" });
   assert.equal(new URL(page.url()).pathname, "/map");
 
+  // The selected destination is marked by a box on all four sides, so a rule
+  // that drops one edge (the mobile nav used to lose its bottom border) is a
+  // regression even though the tab still reads as "active".
+  const activeTab = await page.evaluate(() => {
+    const style = getComputedStyle(document.querySelector(".tab-bar-nav .tab.active"));
+    return ["Top", "Right", "Bottom", "Left"].map((side) => ({
+      width: style.getPropertyValue(`border-${side.toLowerCase()}-width`),
+      color: style.getPropertyValue(`border-${side.toLowerCase()}-color`),
+    }));
+  });
+  for (const edge of activeTab) {
+    assert.notEqual(edge.width, "0px", `active tab border: ${JSON.stringify(activeTab)}`);
+    assert.ok(!/rgba\(0, 0, 0, 0\)|transparent/.test(edge.color), `active tab border: ${JSON.stringify(activeTab)}`);
+  }
+
   // The map is full-bleed: it breaks out of the centred .card column and
   // reaches both viewport edges, without pushing the page sideways.
   const stage = await page.evaluate(() => {