feat(pathanalyzer): map view polish - channel label, auto path, 45vh map

- Show the channel name (dimmed, next to the sender) on map-view tiles
- Clicking a message now auto-selects and draws its shortest routed echo
  (fewest hops, ties -> first); re-clicking keeps the user's echo choice
- Mobile: map takes a fixed 45% of the viewport height and the path list
  gets the remaining space (was min 300px map / max 40% list)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/static/js/path-analyzer.js

@@ -688,6 +688,18 @@ function paBuildLegend(echo) {
     return legend;
 }
 
+// Default echo selection: the routed echo with the fewest hops
+// (ties -> first in arrival order)
+function paShortestEchoIdx(msg) {
+    let best = null;
+    msg.echoView.forEach((echo, idx) => {
+        if (echo.hops > 0 && (best === null || echo.hops < msg.echoView[best].hops)) {
+            best = idx;
+        }
+    });
+    return best;
+}
+
 function paRenderMapView() {
     paInitMap();
     paPlotBaseMarkers();
@@ -715,13 +727,21 @@ function paRenderMapView() {
 
         const head = document.createElement('div');
         head.className = 'd-flex justify-content-between gap-2';
+        const left = document.createElement('div');
+        left.className = 'd-flex align-items-baseline gap-1';
+        left.style.minWidth = '0';
         const senderEl = document.createElement('strong');
         senderEl.className = 'text-truncate';
         senderEl.textContent = msg.sender || '—';
+        const chanEl = document.createElement('span');
+        chanEl.className = 'pa-map-msg-chan';
+        chanEl.textContent = msg.channel_name || `#${msg.channel_idx}`;
+        left.appendChild(senderEl);
+        left.appendChild(chanEl);
         const timeEl = document.createElement('span');
         timeEl.className = 'text-muted text-nowrap';
         timeEl.textContent = paFormatTime(msg).slice(5, 16);
-        head.appendChild(senderEl);
+        head.appendChild(left);
         head.appendChild(timeEl);
         entry.appendChild(head);
 
@@ -735,7 +755,9 @@ function paRenderMapView() {
         }
 
         entry.addEventListener('click', () => {
-            paMapSelection = { msgId: msg.id, echoIdx: null };
+            // Re-clicking the selected message keeps the user's echo choice
+            if (paMapSelection.msgId === msg.id) return;
+            paMapSelection = { msgId: msg.id, echoIdx: paShortestEchoIdx(msg) };
             paRenderMapView();
         });
 

app/templates/path-analyzer.html

@@ -125,11 +125,19 @@
                 flex-direction: column;
             }
 
+            /* Message/path list gets the remaining space, the map keeps a
+               fixed ~45% of the viewport height */
             #paMapSidebar {
                 width: auto;
                 min-width: 0;
-                max-height: 40%;
-                flex-shrink: 1;
+                max-height: none;
+                flex: 1 1 0;
+                min-height: 0;
+            }
+
+            #paMap {
+                flex: 0 0 45vh;
+                min-height: 0;
             }
         }
 
@@ -364,6 +372,12 @@
             color: #6f42c1;
         }
 
+        .pa-map-msg-chan {
+            font-size: 0.72rem;
+            color: var(--text-secondary, #6c757d);
+            white-space: nowrap;
+        }
+
         .pa-map-msg-preview {
             font-size: 0.75rem;
             color: var(--text-secondary, #6c757d);