style(ui): rework light/dark theme to make it visually consistent

Rework the color system around warm neutrals and route hardcoded
surfaces through theme tokens for consistency.

- Theme tokens (index.css, ThemeContext): warm cream light mode and
  neutral charcoal dark mode, replacing the pure-white/blue-tinted
  palette; update PWA theme-color meta
- Code blocks: soft grey background in light mode via
  oneLight/oneDark, and drop the Tailwind Typography <pre> shell that
  framed the highlighter in a dark box
- Dropdowns/panels: convert CommandMenu, Quick Settings, and the JSON
  response block from hardcoded gray/slate to popover/muted/border
  tokens
- Git panel: Publish button purple -> primary blue
- Composer: drop top padding so the input sits flush with the thread

src/components/code-editor/view/subcomponents/markdown/MarkdownCodeBlock.tsx

@@ -1,8 +1,9 @@
 import { useState } from 'react';
 import type { ComponentProps } from 'react';
 import { Prism as SyntaxHighlighter } from 'react-syntax-highlighter';
-import { oneDark as prismOneDark } from 'react-syntax-highlighter/dist/esm/styles/prism';
+import { oneDark as prismOneDark, oneLight as prismOneLight } from 'react-syntax-highlighter/dist/esm/styles/prism';
 import { copyTextToClipboard } from '../../../../../utils/clipboard';
+import { useTheme } from '../../../../../contexts/ThemeContext';
 
 type MarkdownCodeBlockProps = {
   inline?: boolean;
@@ -16,6 +17,7 @@ export default function MarkdownCodeBlock({
   node: _node,
   ...props
 }: MarkdownCodeBlockProps) {
+  const { isDarkMode } = useTheme();
   const [copied, setCopied] = useState(false);
   const rawContent = Array.isArray(children) ? children.join('') : String(children ?? '');
   const looksMultiline = /[\r\n]/.test(rawContent);
@@ -50,20 +52,22 @@ export default function MarkdownCodeBlock({
               setTimeout(() => setCopied(false), 2000);
             }
           })}
-        className="absolute right-2 top-2 z-10 rounded-md border border-gray-600 bg-gray-700/80 px-2 py-1 text-xs text-white opacity-0 transition-opacity hover:bg-gray-700 group-hover:opacity-100"
+        className="absolute right-2 top-2 z-10 rounded-md border border-border bg-card/90 px-2 py-1 text-xs text-foreground/80 opacity-0 transition-opacity hover:bg-muted group-hover:opacity-100"
       >
         {copied ? 'Copied!' : 'Copy'}
       </button>
 
       <SyntaxHighlighter
         language={language}
-        style={prismOneDark}
+        style={isDarkMode ? prismOneDark : prismOneLight}
         customStyle={{
           margin: 0,
-          borderRadius: '0.5rem',
+          borderRadius: '0.75rem',
           fontSize: '0.875rem',
           padding: language !== 'text' ? '2rem 1rem 1rem 1rem' : '1rem',
+          ...(isDarkMode ? {} : { background: 'hsl(var(--muted))' }),
         }}
+        codeTagProps={{ style: isDarkMode ? {} : { background: 'transparent' } }}
       >
         {rawContent}
       </SyntaxHighlighter>

src/components/code-editor/view/subcomponents/markdown/MarkdownPreview.tsx

@@ -12,6 +12,9 @@ type MarkdownPreviewProps = {
 
 const markdownPreviewComponents: Components = {
   code: MarkdownCodeBlock,
+  // MarkdownCodeBlock renders its own highlighted <pre>; passthrough prevents a
+  // second Typography-styled <pre> shell from framing it.
+  pre: ({ children }) => <>{children}</>,
   blockquote: ({ children }) => (
     <blockquote className="my-2 border-l-4 border-gray-300 pl-4 italic text-gray-600 dark:border-gray-600 dark:text-gray-400">
       {children}