[fix](trx-frontend-http): require bidirectional decodes for map QSO contact paths

A QSO requires both parties to hear each other. Previously the map drew
contact paths whenever A sent a directed message to B and B's locator
was known from any message. Now paths only appear when both A→B and B→A
directed messages are present in the decoded history.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -6319,7 +6319,11 @@ function rebuildDecodeContactPaths() {
       }
     }
   }
+  // Index directed messages by "SOURCE::TARGET" for QSO (bidirectional) check
+  const directedPairs = new Set(directedMessages.map((m) => `${m.source}::${m.target}`));
   for (const msg of directedMessages) {
+    // A true QSO requires both A→B and B→A directed messages
+    if (!directedPairs.has(`${msg.target}::${msg.source}`)) continue;
     const targetLocator = stationLocators.get(msg.target);
     if (!targetLocator) continue;
     if (msg.sourceGrid === targetLocator.grid) continue;