Restrict Verify integrity file picker to .sha256 files only

Add input.accept='.sha256' to limit file picker to .sha256 files,
plus an onchange guard that rejects non-.sha256 selections (fallback
for browsers like macOS Safari that ignore custom extensions in accept).

https://claude.ai/code/session_01HnKMFA576NFwa2RzB8vCqE

Author: claude

Services/HtmlReport/diff_report.js

@@ -149,12 +149,17 @@
     }
     var input = document.createElement('input');
     input.type = 'file';
+    input.accept = '.sha256';
     input.style.display = 'none';
     document.body.appendChild(input);
     input.onchange = async function() {
       var file = input.files[0];
       document.body.removeChild(input);
       if (!file) return;
+      if (!file.name.endsWith('.sha256')) {
+        alert('Please select a .sha256 file.');
+        return;
+      }
       var sha256Text = await file.text();
       var match = sha256Text.match(/^([0-9a-f]{64})\b/i);
       if (!match) {

doc/samples/diff_report.html

@@ -1093,12 +1093,17 @@ <h2 style="color:#0051c3">[ ! ] Modified Files &#x2014; Timestamps Regressed (5)
     }
     var input = document.createElement('input');
     input.type = 'file';
+    input.accept = '.sha256';
     input.style.display = 'none';
     document.body.appendChild(input);
     input.onchange = async function() {
       var file = input.files[0];
       document.body.removeChild(input);
       if (!file) return;
+      if (!file.name.endsWith('.sha256')) {
+        alert('Please select a .sha256 file.');
+        return;
+      }
       var sha256Text = await file.text();
       var match = sha256Text.match(/^([0-9a-f]{64})\b/i);
       if (!match) {