Switch English serif from Vollkorn to Crimson Pro

Vollkorn read as too chunky next to the Malayalam bio in Manjari.
Crimson Pro is a calmer book-face serif that pairs more evenly.

Renames the CSS variable from --vk to --serif to reflect that the
value is no longer Vollkorn-specific, and bumps .ml to 17px/1.5
so the Malayalam subtitle sits at a comfortable reading size.

templates/upload.html

@@ -4,7 +4,7 @@
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>Upload — Photo Gallery</title>
-  <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Vollkorn:ital,wght@0,400;0,600;0,700;1,400&family=Manjari:wght@100;400;700&display=swap">
+  <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Crimson+Pro:ital,wght@0,400;0,600;0,700;1,400&family=Manjari:wght@100;400;700&display=swap">
   <link rel="stylesheet" href="/static/style.css">
   <style>
     .upload-page {
@@ -13,7 +13,7 @@
       padding: 32px 20px;
     }
     .upload-page h2 {
-      font-family: var(--vk);
+      font-family: var(--serif);
       font-size: 22px;
       font-weight: 600;
       color: var(--fg);
@@ -53,7 +53,7 @@
       color: var(--fg4);
       pointer-events: none;
     }
-    .drop-prompt p  { font-size: 14px; font-family: var(--vk); }
+    .drop-prompt p  { font-size: 14px; font-family: var(--serif); }
     .drop-prompt small { font-size: 12px; font-family: monospace; }
     #preview {
       display: none;
@@ -84,7 +84,7 @@
       outline: none;
       transition: border-color 0.2s;
     }
-    .field input[type="text"]  { font-family: var(--vk); }
+    .field input[type="text"]  { font-family: var(--serif); }
     .field input[type="date"]  { font-family: monospace; font-size: 14px; color-scheme: dark; }
     .field input:focus { border-color: var(--fg4); }
     .submit-btn {
@@ -92,7 +92,7 @@
       background: var(--bg1);
       border: 1px solid var(--bg2);
       color: var(--fg2);
-      font-family: var(--vk);
+      font-family: var(--serif);
       font-size: 16px;
       font-weight: 600;
       padding: 12px;