feat: expand to Tibetan + Theravada — 10 masters across 三大传统 (v0.4)

Adds the project's first non-Chinese masters, taking the scope from
"Chinese Buddhist" to "Buddhist" and matching the project name's
broader implication.

New masters
-----------
• prebuilt/milarepa — Tibetan Kagyu yogi (1052–1135). Sources:
  The Hundred Thousand Songs of Milarepa (mGur 'bum, BDRC W1KG14334)
  and The Life of Milarepa (rNam thar, BDRC W22272). Coverage:
  Mahāmudrā view, Naro Chodruk (name-level only — no esoteric steps),
  retreat & austerity, guru yoga, karma & purification.

• prebuilt/ajahn-chah — Thai Forest Tradition founder of Wat Pah Pong
  (1918–1992). Sources: Pali Canon (SuttaCentral SC IDs) plus
  authorized English collections Food for the Heart, A Still Forest
  Pool, Living Dhamma. Coverage: sati & satipaṭṭhāna, ānāpānasati,
  three characteristics, letting go, sīla-samādhi-paññā, middle way.

HARD-GATE additions
-------------------
• no_esoteric_instruction — Tibetan tantric practice steps (tummo,
  generation/completion stages, empowerment-required visualizations
  and mantras) are never disclosed; queries are redirected to
  qualified teachers. Boundary registered in
  scripts/validate-fidelity.py.

• No fabricated quotes for Theravāda discourses — Ajahn Chah quotes
  must trace to authorized publications; no synthesized "Ajahn Chah
  said" dialogue.

Citation system
---------------
BDRC:Wxxxxx (Tibetan canon) and SuttaCentral SC IDs are now
first-class alongside CBETA Txxnxxxx in frontmatter sources lists.
validate.py already accepts non-cbeta sources via the existing
title-or-cbeta_id check, no schema change required.

Cross-tradition compare-masters mappings
----------------------------------------
prebuilt/compare/SKILL.md gets new fallback rows for: 苦行/闭关
(xuyun + milarepa), 正念/觉知 (huineng + ajahn-chah + xuyun),
出离心/无常 (yinguang + milarepa + ajahn-chah), 三大传统对比
(huineng + milarepa + ajahn-chah), and adds milarepa to 般若/空性,
ajahn-chah to 戒律/行持.

Surface updates
---------------
• Description across package.json, .claude-plugin/{plugin,marketplace}.json,
  .cursor-plugin/plugin.json: "Chinese Buddhist" → "Buddhist",
  "8 prebuilt masters" → "10 prebuilt masters across 汉传/藏传/南传".
• README.md + README_EN.md: cross-tradition rows in the situational
  guidance table; new master cards for Milarepa and Ajahn Chah with
  appropriate provenance notes; v0.4 release banner replaces v0.3.
• SKILL.md preset list reorganized by tradition.
• CHANGELOG.md gets a [0.4.0] section.
• package.json keywords add tibetan-buddhism, theravada, bdrc,
  suttacentral.

Validation
----------
• python scripts/validate.py --strict → ✅ 11 masters pass
• python scripts/validate-fidelity.py → ✅ 11 masters validated
  (12 + 13 fidelity cases for the two new masters)
• python scripts/test-fidelity.py --all --dry-run → ✅
• pytest tests/ → ✅ 31 passed, 6 skipped

The progressive-disclosure shape of v0.3 is preserved exactly, so
the fidelity-smoke CI cost cap is unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

prebuilt/milarepa/sources/INDEX.md

@@ -0,0 +1,24 @@
+# 米拉日巴尊者 Sources 索引
+
+本目录为离线可用的藏文典籍片段，对应本 master 引用的核心传承文献。
+
+## 收录文件
+
+| 文件 | 来源典籍 | BDRC | 覆盖主题 |
+|---|---|---|---|
+| `grubum-excerpts.md` | 《米拉日巴道歌集》（十万歌集，mGur 'bum） | [W1KG14334](https://library.bdrc.io/show/bdr:W1KG14334) | 大手印见地、出离、闭关、上师瑜伽、觉受 vs 证悟 |
+| `namthar-excerpts.md` | 《密勒日巴尊者传》（rNam thar） | [W22272](https://library.bdrc.io/show/bdr:W22272) | 早年罪业、玛尔巴折磨、雪山苦行、降魔、涅槃 |
+
+## 引用规范
+
+- 格式：`【《典籍名》§章节】（BDRC: Wxxxxx）`
+- 示例：`【《米拉日巴道歌集·与猎人贡波多杰之歌》】（BDRC: W1KG14334）`
+
+## 说明
+
+- 所有片段节选自 BDRC（Buddhist Digital Resource Center）公开元数据所对应的藏文典籍
+- 汉译参考：张澄基《密勒日巴大师全集》（慧炬出版社）
+- 英译参考：Garma C. C. Chang, *The Hundred Thousand Songs of Milarepa*; Andrew Quintman, *The Life of Milarepa* (Penguin Classics)
+- 用于教学引用，不代表完整经义；深入研究请查阅 BDRC、84000、Lotsawa House 全本
+- **密法相关章节本目录刻意不收录**（拙火、那洛六法、生起圆满次第具体修法步骤），密法须依止具格上师亲传
+- 增补片段欢迎 PR