docs(web): describe the prompt anchor rail as it is built

The setting hint and the composable comment still promised a proportional
TOC with a viewport indicator. The rail draws one tick per prompt and marks
the tick nearest the middle of the view.

Author: elkaix

apps/pythinker-web/src/composables/usePythinkerWebClient.ts

@@ -703,7 +703,7 @@ function setUiFontSize(value: number): void {
 }
 
 // ---------------------------------------------------------------------------
-// Beta: proportional conversation TOC with viewport indicator and hover tooltip.
+// Beta: prompt anchor rail — one tick per user prompt, with a hover tooltip.
 // Default on; persisted per browser.
 // ---------------------------------------------------------------------------
 const BETA_TOC_STORAGE_KEY = 'pythinker-web.beta-toc';

apps/pythinker-web/src/i18n/locales/en/settings.ts

@@ -58,5 +58,5 @@ export default {
   exportLogBtn: 'Export log',
   beta: 'Experimental',
   betaToc: 'Prompt anchor rail',
-  betaTocHint: ' Prompt ticks, viewport indicator, and reply previews',
+  betaTocHint: ' Prompt ticks with hover previews, active tick follows the view',
 };