feat(onboarding): browser-first README + starter_questions for 8 masters

Shift the README narrative so that non-developer users — the 99% of the
actual audience — find the browser entry point first and the CLI install
second. The old structure buried fojin.app/chat at line 48 under a wall
of developer badges.

Changes:

- README.md / README_EN.md: new "立即体验 / Try It Now" hero section
  right after the title block, with a big call-to-action linking to
  fojin.app/chat, a "which master should I ask" recommendation table,
  and an explicit redirect for CLI users to the developer section.
- Rename "快速开始 / Quick Start" → "开发者安装 / Developer Installation"
  with a clear "if you just want to try it, use the browser instead"
  callout at the top.
- Update TOC anchors in both languages to match.

- prebuilt/<master>/meta.json × 8: new `starter_questions` field with
  4 Q&A entries per master. Each entry has `q` (the question) and `why`
  (why this question is suited for this specific master's voice and
  source corpus). Intended consumer: fojin.app/chat can fetch the raw
  meta.json on master selection and render these as cold-start prompts
  — solving the empty-input-box problem for first-time users.

Rationale: the biggest onboarding gap for non-CLI users is "I don't
know what to ask this master." A curated 4-question starter per master
provides both a safe entry point and a teaching signal about what this
particular master is actually good at answering.

Validated: scripts/validate.py --strict passes (9/9 masters).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

prebuilt/huineng/meta.json

@@ -69,5 +69,23 @@
       "菩提",
       "弘忍"
     ]
-  }
+  },
+  "starter_questions": [
+    {
+      "q": "六祖说'本来无一物'，但烦恼和身体明明还在，这不是自欺吗？",
+      "why": "直切禅门最容易被误解的核心悖论"
+    },
+    {
+      "q": "我想参禅但坐不住、念头太多，该怎么办？",
+      "why": "《坛经》中有针对妄念的直接对治方便"
+    },
+    {
+      "q": "'见性成佛'的'见'是看见吗？是悟吗？具体是什么体验？",
+      "why": "触及禅宗实修的核心目标，避免把'见性'变成概念游戏"
+    },
+    {
+      "q": "读经和参禅哪个更重要？六祖不识字怎么讲法？",
+      "why": "历史上反复被问的问题，直接听当事人的答案"
+    }
+  ]
 }