Fix file switching blocked by stale dirty state from previous file

When navigating via sidebar while editing a file, the global editorDirty
flag from the previous file incorrectly triggered the "File changed on
disk" defer logic for the newly opened file. Skip the defer check for
intentional frontend navigations and reset dirty state on switch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lightsofapollo

web/src/App.svelte

@@ -914,10 +914,13 @@
         pruneTabsForRemovedPaths(removedPaths);
       }
       if (detectFileType(data.filePath) === 'markdown' && typeof data.markdown !== 'string') {
-        if (mode === 'edit' && data.filePath === activePath && editorDirty) {
+        if (!wasFrontendNav && mode === 'edit' && data.filePath === activePath && editorDirty) {
           deferExternalReload(data.filePath, data.contentMtimeMs);
           return;
         }
+        if (wasFrontendNav) {
+          editorDirty = false;
+        }
         void loadMarkdownForPath(data.filePath, data.contentMtimeMs);
       }
     }