webui: dark mode support to demo fmwk, tool cards

Demo framework fixes:
- sketch-push-button.demo.ts: add dark variants for bg, border, text colors
- chat-input.ts: add dark variants for message containers and status sections
- demo-runner.ts: replace inline error styles with Tailwind dark mode classes
- sketch-call-status.demo.ts: fix hardcoded white backgrounds in status cards
- sketch-diff-range-picker.demo.ts: add dark variants to picker and status displays
- sketch-timeline-message.demo.ts: fix message container backgrounds
- sketch-view-mode-select.demo.ts: comprehensive dark mode for all scenarios

Tool card fixes:
- Update shared createPreElement function with dark:bg-gray-700/dark:text-gray-100
- bash tool: fix command display and result areas
- think tool: fix input content area with proper dark background
- patch tool: comprehensive diff rendering with dark variants for added/removed/context lines
- codereview tool: inherits dark mode through shared utilities

All components now use consistent dark mode patterns with proper contrast:
bg-white dark:bg-gray-800, border-gray-200 dark:border-gray-700,
text-gray-600 dark:text-gray-300, matching existing components.

Co-Authored-By: sketch <hello@sketch.dev>
Change-ID: s8ac5253d0cbaa3ack
diff --git a/webui/src/web-components/demo/sketch-push-button.demo.ts b/webui/src/web-components/demo/sketch-push-button.demo.ts
index f7b83fd..4405a9e 100644
--- a/webui/src/web-components/demo/sketch-push-button.demo.ts
+++ b/webui/src/web-components/demo/sketch-push-button.demo.ts
@@ -12,18 +12,20 @@
   render() {
     return html`
       <div
-        class="p-4 bg-white rounded-lg shadow-sm border border-gray-200 max-w-md mx-auto"
+        class="p-4 bg-white dark:bg-gray-800 rounded-lg shadow-sm border border-gray-200 dark:border-gray-700 max-w-md mx-auto"
       >
-        <h2 class="text-lg font-semibold mb-4">Push Button Demo</h2>
+        <h2 class="text-lg font-semibold mb-4 text-gray-900 dark:text-gray-100">
+          Push Button Demo
+        </h2>
 
         <div class="mb-4">
-          <p class="text-sm text-gray-600 mb-2">
+          <p class="text-sm text-gray-600 dark:text-gray-300 mb-2">
             Test the push button component:
           </p>
           <sketch-push-button></sketch-push-button>
         </div>
 
-        <div class="text-xs text-gray-500">
+        <div class="text-xs text-gray-500 dark:text-gray-400">
           <p>Click the push button to test:</p>
           <ul class="list-disc list-inside mt-1">
             <li>Modal opens with git information</li>