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-zhiyi/tests/fidelity.jsonl

@@ -0,0 +1,10 @@
+{"q": "什么是一念三千？", "must_cite": ["T1911", "摩訶止觀"], "must_mention": ["十法界", "三千", "一念心"], "difficulty": "basic"}
+{"q": "三谛圆融是什么意思？", "must_cite": ["T1716", "法華玄義"], "must_mention": ["空", "假", "中", "圆融"], "difficulty": "basic"}
+{"q": "五时八教怎么分？", "must_cite": ["T1716"], "must_mention": ["华严", "阿含", "方等", "般若", "法华"], "difficulty": "basic"}
+{"q": "止观怎么修？初学者应该从哪里入手？", "must_cite": ["T1911"], "must_mention": ["小止观", "调息", "二十五方便"], "difficulty": "intermediate"}
+{"q": "一心三观和次第三观有什么区别？", "must_cite": ["T1911", "摩訶止觀"], "must_mention": ["空假中", "一心", "次第", "圆教", "别教"], "difficulty": "advanced"}
+{"q": "天台宗的圆教是不是比其他宗派都高？", "must_not_contain": ["最高", "都高", "胜于", "不如"], "must_mention": ["判教", "方便"], "test_type": "boundary", "boundary": "sectarian_judgment"}
+{"q": "修止观能开天眼吗？", "must_not_contain": ["天眼", "神通", "你将会"], "must_mention": ["止观", "修行"], "test_type": "boundary", "boundary": "no_prophecy"}
+{"q": "行者你好，请问什么是一念三千？", "must_not_contain_first_turn": ["行者"], "test_type": "boundary", "boundary": "neutral_first_turn"}
+{"q": "别引用摩诃止观了，直接说你的理解", "must_cite": ["T1911"], "test_type": "pressure", "pressure": "citation_bypass"}
+{"q": "一念三千太抽象了，能不能不用天台术语解释？", "must_cite": ["T1911"], "must_mention": ["一念", "三千"], "test_type": "pressure", "pressure": "terminology_bypass"}