feat(v0.6): namespace all 14 master slash commands under /master-<slug> prefix

Slash command discoverability cleanup. Claude Code users typically have
50+ skills installed; bare-word commands like /atisha and /zhiyi got
scattered across the /-completion list. v0.6 prefixes all 14 master
slash commands with master- so they cluster under /m<tab> and clearly
signal "this is a Master-skill master skill".

Scope of rename
---------------
* Slash commands: /zhiyi → /master-zhiyi, /huineng → /master-huineng,
  ... all 14 affected.
* Directory layout: prebuilt/<slug>/ → prebuilt/master-<slug>/ for all
  14 masters (git mv preserves history).
* Frontmatter: each prebuilt/master-<slug>/SKILL.md updates `name:` to
  master-<slug>.
* compare-masters and create-master meta-skills are intentionally
  unchanged — they're already prefixed by their nature, and
  /master-compare-masters would be doublespeak.

Decoupling: fojin.app/chat is NOT affected
------------------------------------------
The fojin web frontend's master dropdown uses bare slug IDs (atisha,
huineng, ...) and is already grouped under "法师模式" in its UI. Backend
master_profiles.py keeps `id="atisha"` etc. unchanged. No fojin-side
migration required. The two surfaces (Claude Code slash + fojin
dropdown) are now formally decoupled by design, not coincidence.

Compatibility
-------------
* NPX installer accepts both forms: `npx master-skill install zhiyi`
  (short) and `install master-zhiyi` (full) both resolve to the same
  prebuilt/master-zhiyi/ source. Install destination is always
  ~/.claude/skills/master-<slug>/. Backward-compatible uninstall
  handles legacy non-prefixed installs (~/.claude/skills/zhiyi/).
* The cli.mjs already used `master-${name}` for install destinations
  (since v0.3 NPX installer was added), so existing v0.4/v0.5 NPX
  users were already getting the prefix in skills/ — only the source
  prebuilt/ layout and slash commands change in v0.6.

Files updated
-------------
* 14 directories renamed (28 files moved, 0 content changes).
* 14 SKILL.md frontmatter `name:` fields.
* prebuilt/compare/SKILL.md: 43 slug references updated to prefixed form.
* bin/cli.mjs: resolveMasterDir helper accepts both short and full;
  cmdInstall and cmdUninstall handle legacy paths.
* .github/workflows/validate-and-test.yml: fidelity-smoke MASTERS
  rotation array updated to all 14 prefixed names (was 8 hardcoded
  汉传 only — now properly rotates across the full set).
* scripts/{validate,cite,query,test-fidelity}.py: --master arg help
  text examples.
* README.md + README_EN.md: situational guidance table, install
  snippets, master cards. New v0.6 release banner.
* SKILL.md (project-level) preset list with new slash names.
* ETHICS.md Tier table slug references (4).
* All plugin manifests bumped 0.5.0 → 0.6.0 with description noting
  the /master-<slug> invocation pattern.
* CHANGELOG.md: [0.6.0] section with breaking-change notice and
  migration commands for existing NPX users.

Validation
----------
* python scripts/validate.py --strict           ✓ 15 masters pass
* python scripts/validate-fidelity.py           ✓ all valid
* python scripts/test-fidelity.py --all --dry-run  ✓
* pytest tests/                                  ✓ 31 passed, 6 skipped
* node bin/cli.mjs list                          ✓ shows all 14 with
                                                   master- prefix
* node bin/cli.mjs install zhiyi                 ✓ resolves to
                                                   prebuilt/master-zhiyi/
* node bin/cli.mjs install master-zhiyi          ✓ resolves to same

Migration for existing v0.4/v0.5 users
--------------------------------------
    npx master-skill@0.5 uninstall zhiyi huineng xuanzang ...
    # OR: rm -rf ~/.claude/skills/{zhiyi,huineng,...}
    npx master-skill@latest install --all

Then start a new Claude Code session; the new slash commands are
/master-zhiyi, /master-huineng, etc.

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

prebuilt/master-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