Merge #720: fix(log-viewer): stop reconnecting after a startup error

The floating log viewer reconnected every few seconds when its tail-file
stream ended with a startup error (path refused, file missing, too large,
stream limit, tail spawn failure). It now closes the EventSource on an
`error` message that arrives before `connected`; an established stream
keeps its reconnect.

Squashed from #720 (johoja12). Maintainer edits while landing, as the
review said: the onerror close is dropped (it stopped the browser's own
retry after a transport failure, leaving the window on "Connecting"),
the test's check for a button nothing renders is gone, and the stubbed
stream sets `retry: 200` so a reconnect, if one came, shows within the
shorter wait.

Co-authored-by: Codeman maintainer <kay@stutz.science>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/web/public/panels-ui.js

@@ -6163,6 +6163,7 @@ Object.assign(CodemanApp.prototype, {
       CodemanBase.url(`/api/sessions/${sessionId}/tail-file?path=${encodeURIComponent(filePath)}&lines=50`)
     );
 
+    let connected = false;
     eventSource.onmessage = (e) => {
       const data = JSON.parse(e.data);
       const body = document.getElementById(`log-viewer-body-${windowId}`);
@@ -6170,6 +6171,7 @@ Object.assign(CodemanApp.prototype, {
 
       switch (data.type) {
         case 'connected':
+          connected = true;
           body.innerHTML = '';
           break;
         case 'data':
@@ -6189,6 +6191,7 @@ Object.assign(CodemanApp.prototype, {
           this.updateLogViewerStatus(windowId, 'disconnected', 'ended');
           break;
         case 'error':
+          if (!connected) eventSource.close();
           body.innerHTML += `<div class="log-error">${escapeHtml(data.error)}</div>`;
           this.updateLogViewerStatus(windowId, 'error', 'error');
           break;