[feat](trx-frontend-http): reorder plugin tabs and add FT8 slot timer

Reorder Plugins subtabs to align with the Overview plugin listing
(APRS, CW, FT8, WSPR), with Map moved to the end.

Also add a live FT8 period countdown indicator in the FT8 panel.

Co-authored-by: Codex <codex@openai.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/ft8.js

@@ -1,8 +1,10 @@
 // --- FT8 Decoder Plugin (server-side decode) ---
 const ft8Status = document.getElementById("ft8-status");
+const ft8PeriodEl = document.getElementById("ft8-period");
 const ft8MessagesEl = document.getElementById("ft8-messages");
 const ft8FilterInput = document.getElementById("ft8-filter");
 const FT8_MAX_MESSAGES = 200;
+const FT8_PERIOD_SECONDS = 15;
 let ft8FilterText = "";
 
 function fmtTime(tsMs) {
@@ -10,6 +12,16 @@ function fmtTime(tsMs) {
   return new Date(tsMs).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit", second: "2-digit" });
 }
 
+function updateFt8PeriodTimer() {
+  if (!ft8PeriodEl) return;
+  const nowSec = Math.floor(Date.now() / 1000);
+  const remaining = FT8_PERIOD_SECONDS - (nowSec % FT8_PERIOD_SECONDS);
+  ft8PeriodEl.textContent = `Next slot ${String(remaining).padStart(2, "0")}s`;
+}
+
+updateFt8PeriodTimer();
+setInterval(updateFt8PeriodTimer, 500);
+
 function renderFt8Row(msg) {
   const row = document.createElement("div");
   row.className = "ft8-row";