Add delete, inline preview, and mobile list layout to the file browser

- DELETE /files/{path} recursively removes a file/folder (root itself
  can't be deleted, 404 on missing paths); wired to a new "Delete"
  action in the web UI with a confirmation prompt.
- Files now open inline (Content-Disposition: inline) so browsers can
  play/preview natively-supported types (video, audio, images, PDF)
  directly instead of always forcing a download. A separate
  "Download" link (?download=1) still forces a save-as.
- Narrow screens get a stacked card list (name, size, modified date,
  download/delete actions) instead of a squeezed table, so nothing is
  hidden or requires horizontal scrolling; the table layout is kept
  unchanged for sm+ screens.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

web/static/files.js

@@ -84,6 +84,28 @@
             setStatus(`Could not create folder: ${String(err)}`);
         }
     });
+    document.querySelectorAll(".delete-entry-button").forEach((button) => {
+        button.addEventListener("click", async () => {
+            const relPath = button.dataset.path || "";
+            const name = button.dataset.name || relPath;
+            if (!window.confirm(`Delete "${name}"? This cannot be undone.`)) {
+                return;
+            }
+            setStatus(`Deleting "${name}"…`);
+            try {
+                const resp = await fetch(`/web/files/${relPath}`, { method: "DELETE" });
+                if (!resp.ok) {
+                    const text = await resp.text();
+                    setStatus(`Could not delete "${name}": ${text}`);
+                    return;
+                }
+                window.location.reload();
+            }
+            catch (err) {
+                setStatus(`Could not delete "${name}": ${String(err)}`);
+            }
+        });
+    });
     // Recursively walk a dropped DataTransferItem (file or directory) into
     // a flat list of File objects, using the browser's non-standard but
     // widely-supported webkitGetAsEntry/FileSystemEntry APIs to support