feat: refine the reviewer explorer and the visual system

- Explorer: redacted terms are highlighted in Markdown and code, the
  sidebar shows when the link expires, "Download repository" is the one
  primary action, and signed-out reviewers get a header without Sign in
  or the source-code link.
- Status: a ready anonymization leads with a copyable share link; the
  support links sit flat inside their section.
- One primary colour (accent) for actions and progress; mono is kept for
  IDs, hashes and paths; settings are plain sections instead of cards.
- Font sizes snap to one scale (10-40px); rem values keep following the
  reader's browser font size.
- Ko-fi button uses a dark surface in dark mode instead of a white pill.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

public/index.html

@@ -86,11 +86,9 @@
             type: "floating-chat",
             "floating-chat.donateButton.text": "Support me",
             "floating-chat.donateButton.background-color": isDark
-              ? "#FAF9F6"
+              ? "#34312C"
               : "#1A1815",
-            "floating-chat.donateButton.text-color": isDark
-              ? "#1A1815"
-              : "#FAF9F6",
+            "floating-chat.donateButton.text-color": "#FAF9F6",
           });
         };
         document.body.appendChild(s);