feat(browse): extension chip under tree icon + archive refs in hovercard

Two small surface upgrades on file rows:

- Tree icon column now stacks the Lucide glyph on top of a small
  uppercase extension chip (PDF, DOCX, YAML, etc.). File type reads
  at a glance without expanding the row. Folders and zips skip the
  chip — their glyph already carries enough.
- Hovercard on a ZDDC-parseable file gains two clickable references
  in the .archive section:
    Latest         → /<project>/.archive/<tracking>.html
    This revision  → /<project>/.archive/<tracking>_<rev>.html
  Both forms are dispatcher-canonicalised to project-root, so the
  link works from any depth. Folders that parse (transmittal folders)
  get just the Latest link.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

browse/css/tree.css

@@ -361,15 +361,17 @@ body {
 
 .tree-name__icon {
     flex-shrink: 0;
-    /* Fixed-width column keeps label alignment consistent regardless
+    /* Stacked column — glyph on top, extension chip below for files.
-       of which symbol the row picks. Height matches one line of label
+       Wider min-width than the 1em glyph itself so common extensions
-       text so the icon anchors to the title row on two-line layouts. */
+       (pdf/docx/xlsx/json) don't push the label sideways. Height
-    width: 1.2em;
+       grows with content; flex-start anchors to the title-line. */
-    height: 1.2em;
+    min-width: 2.2em;
     display: inline-flex;
+    flex-direction: column;
     align-items: center;
-    justify-content: center;
+    justify-content: flex-start;
     color: var(--text-muted);
+    gap: 1px;
 }
 
 .tree-name__icon svg {
@@ -378,6 +380,19 @@ body {
     display: block;
 }
 
+.tree-name__ext {
+    font-size: 0.58rem;
+    line-height: 1;
+    color: var(--text-muted);
+    text-transform: uppercase;
+    letter-spacing: 0.04em;
+    font-weight: 600;
+    max-width: 100%;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+}
+
 /* Folder rows get the primary accent so directories stand out from
    files at a glance — same convention as macOS Finder / GNOME Files. */
 .tree-row[data-isdir="true"] .tree-name__icon,
@@ -951,6 +966,17 @@ body {
     font-size: 0.78rem;
 }
 
+/* Archive-reference links inside the hovercard pick up the primary
+   accent so they read as clickable, and stay inline with the mono
+   font when they sit inside a mono cell. */
+.tree-hovercard__val a {
+    color: var(--primary, #2868c8);
+    text-decoration: none;
+}
+.tree-hovercard__val a:hover {
+    text-decoration: underline;
+}
+
 /* Separator stretches across both grid columns. Bleed into the
    card's padding so it visually reads as a divider, not a hairline. */
 .tree-hovercard__sep {

browse/js/hovercard.js

@@ -108,6 +108,32 @@
             if (parsed.revision) html += kv('Revision', parsed.revision, true);
             if (parsed.status) html += kv('Status', parsed.status, true);
             if (parsed.title) html += kv('Title', parsed.title);
+
+            // Archive references — the /<project>/.archive/<tracking>.html
+            // URL is the latest issued version (highest base rev), and
+            // /<project>/.archive/<tracking>_<rev>.html pins the exact
+            // revision the user is currently hovering. The dispatcher
+            // canonicalises both forms to project-root so links work
+            // from any depth.
+            if (parsed.trackingNumber) {
+                var fullPath = tree ? tree.pathFor(node) : '';
+                var rel = fullPath.replace(/^\/+|\/+$/g, '');
+                var firstSeg = rel ? rel.split('/')[0] : '';
+                if (firstSeg) {
+                    var encProject  = encodeURIComponent(firstSeg);
+                    var encTracking = encodeURIComponent(parsed.trackingNumber);
+                    var latestUrl   = '/' + encProject + '/.archive/' + encTracking + '.html';
+                    var latestLbl   = '.archive/' + parsed.trackingNumber + '.html';
+                    html += kvLink('Latest', latestUrl, latestLbl);
+                    if (!node.isDir && parsed.revision) {
+                        var encRev      = encodeURIComponent(parsed.revision);
+                        var inspectUrl  = '/' + encProject + '/.archive/' + encTracking + '_' + encRev + '.html';
+                        var inspectLbl  = '.archive/' + parsed.trackingNumber + '_' + parsed.revision + '.html';
+                        html += kvLink('This revision', inspectUrl, inspectLbl);
+                    }
+                }
+            }
+
             html += '<div class="tree-hovercard__sep"></div>';
         } else if (node.displayName) {
             // Operator-supplied display name — only useful as info if
@@ -136,6 +162,18 @@
             + '">' + escapeHtml(val) + '</span>';
     }
 
+    // kvLink — value rendered as an <a> the user can click (opens in
+    // a new tab so the hover context isn't lost) or right-click to
+    // copy. Used for the .archive references on ZDDC files.
+    function kvLink(key, href, label) {
+        return '<span class="tree-hovercard__key">' + escapeHtml(key) + '</span>'
+            + '<span class="tree-hovercard__val tree-hovercard__val--mono">'
+            +   '<a href="' + escapeHtml(href) + '" target="_blank" rel="noopener">'
+            +     escapeHtml(label)
+            +   '</a>'
+            + '</span>';
+    }
+
     function render(node) {
         var z = window.zddc;
         var parsed = z

browse/js/tree.js

@@ -368,6 +368,12 @@
         var virtualHint = node.virtual
             ? '<span class="tree-name__hint">(empty)</span>'
             : '';
+        // Extension chip stacked under the file icon. Files with a
+        // non-empty ext get a small uppercase label; folders / zips
+        // skip it (the chevron + icon glyph carries enough info).
+        var extChip = (!node.isDir && !node.isZip && node.ext)
+            ? '<span class="tree-name__ext">' + escapeHtml(String(node.ext)) + '</span>'
+            : '';
         return ''
             + '<div class="tree-row ' + (visuallyExpanded ? 'expanded' : '') + selected + virtualCls
                 + '" data-id="' + node.id
@@ -377,7 +383,7 @@
                 + ' style="padding-left:' + indent + 'rem"'
                 + ' role="treeitem" tabindex="-1">'
             + '<span class="' + chevronClass + '">' + chevronGlyph + '</span>'
-            + '<span class="tree-name__icon">' + iconChar + '</span>'
+            + '<span class="tree-name__icon">' + iconChar + extChip + '</span>'
             + labelHtml(node)
             + virtualHint
             + '</div>';