fix(browse): markdown editor shrinks instead of overhanging; pop out opens the real editor

- Overflow: the preview pane's child (the markdown shell) was a flex item with
  the default min-width:auto, so the editor's wide internal min-content pushed
  the whole pane past the viewport's right edge. Add min-width:0 on
  .preview-pane__body and its children so the editor shrinks (and its own +
  the grid's minmax(0) scrolling takes over) — the pane never overhangs.
- Pop out: editor-type files (markdown, yaml/.zddc, code text) were popped into
  the lightweight preview window, which can't host the bundled editor — so
  markdown showed as raw <pre>. Now they open the FULL browse app deep-linked
  to the file (<dir>?file=<name>) in a new window, loading the real editor.
  HTML keeps its rendered popup; images/pdf/office unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

browse/css/tree.css

@@ -249,6 +249,7 @@ body {
                                content's natural size (which clips the
                                YAML editor's bottom when there are many
                                lines, even with the editor's own scroll) */
+    min-width: 0;
     overflow: auto;
     display: flex;
     flex-direction: column;
@@ -256,10 +257,16 @@ body {
 }
 
 /* The body's children fill the available space. Plugins inject
-   different content here — img, iframe, pre, custom markdown editor. */
+   different content here — img, iframe, pre, custom markdown editor.
+   min-width:0 is load-bearing: a flex item defaults to min-width:auto
+   (its min-content width), so the markdown editor's wide internal
+   min-content would push the whole pane past the viewport's right edge
+   instead of shrinking. With min-width:0 the editor shrinks and its own
+   (and the grid's minmax(0)) scrolling takes over. */
 .preview-pane__body > * {
     flex: 1;
     min-height: 0;
+    min-width: 0;
 }
 
 .preview-empty {

browse/js/preview.js

@@ -485,6 +485,25 @@
     }
 
     async function renderInPopup(node) {
+        // Editor-type files (markdown, yaml/.zddc, code text) can't be hosted
+        // in the lightweight popup window — they need the bundled editor. Pop
+        // them out as the FULL browse app deep-linked to the file, which loads
+        // the real editor in a new window. Server mode only; HTML keeps its
+        // rendered popup. Falls through to the lightweight popup otherwise.
+        var pext = (node.ext || '').toLowerCase();
+        var ym = window.app.modules.yamledit;
+        var isEditorType = pext === 'md' || pext === 'markdown'
+            || (ym && ym.handles && ym.handles(node) && pext !== 'html' && pext !== 'htm');
+        if (isEditorType && window.app.state.source === 'server' && node.url) {
+            var slash = node.url.lastIndexOf('/');
+            var pdir = slash >= 0 ? node.url.slice(0, slash + 1) : '/';
+            var pbase = slash >= 0 ? node.url.slice(slash + 1) : node.url;
+            var pp = new URLSearchParams();
+            try { pp.set('file', decodeURIComponent(pbase)); } catch (_e) { pp.set('file', pbase); }
+            if (window.app.state.showHidden) pp.set('hidden', '1');
+            window.open(pdir + '?' + pp.toString(), '_blank', 'noopener');
+            return;
+        }
         var info;
         try {
             info = await getBlobUrl(node);