feat(f7): sealed webview asset + esbuild preview bundle (#21)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

media/preview.css

@@ -0,0 +1,53 @@
+/* F7 track-changes preview — theme-aware via VS Code webview CSS variables. */
+body {
+  font-family: var(--vscode-font-family);
+  font-size: var(--vscode-font-size);
+  color: var(--vscode-foreground);
+  background: var(--vscode-editor-background);
+  padding: 0 1.2rem 2rem;
+  line-height: 1.5;
+}
+#cw-header {
+  position: sticky;
+  top: 0;
+  background: var(--vscode-editor-background);
+  border-bottom: 1px solid var(--vscode-panel-border);
+  padding: 0.5rem 0;
+  font-size: 0.85em;
+  opacity: 0.85;
+  display: flex;
+  gap: 1rem;
+}
+#cw-summary .cw-add { color: var(--vscode-gitDecoration-addedResourceForeground); }
+#cw-summary .cw-del { color: var(--vscode-gitDecoration-deletedResourceForeground); }
+.cw-blk { position: relative; }
+ins, .cw-added {
+  background: var(--vscode-diffEditor-insertedTextBackground, rgba(0, 255, 0, 0.15));
+  text-decoration: none;
+}
+del, .cw-removed {
+  background: var(--vscode-diffEditor-removedTextBackground, rgba(255, 0, 0, 0.15));
+  text-decoration: line-through;
+  opacity: 0.7;
+}
+.cw-changed { outline: 2px solid var(--vscode-diffEditor-insertedTextBackground, rgba(0, 255, 0, 0.25)); outline-offset: 2px; }
+.cw-badge {
+  position: absolute;
+  top: 0;
+  right: 0;
+  font-size: 0.7em;
+  padding: 0 0.4em;
+  border-radius: 3px;
+  background: var(--vscode-badge-background);
+  color: var(--vscode-badge-foreground);
+}
+.cw-error {
+  border: 1px solid var(--vscode-inputValidation-errorBorder);
+  background: var(--vscode-inputValidation-errorBackground);
+  color: var(--vscode-errorForeground);
+  padding: 0.3rem 0.6rem;
+  border-radius: 3px;
+  font-size: 0.85em;
+}
+pre.mermaid { text-align: center; background: transparent; }
+pre.mermaid[data-cw-error] { color: var(--vscode-errorForeground); }