chore(governance): add ETHICS.md, CHANGELOG.md, and PR fidelity smoke

Three governance-tier additions to convert Master-skill from a demo into a
defensible long-lived project:

**ETHICS.md** — mandatory governance document:
- AI transparency: outputs are AI-synthesized, not masters' own words
- Copyright tiers A (public domain, current 8), B (in-copyright, needs
  license), C (never admit: living masters, Buddhas/bodhisattvas, apocryphal
  figures), D (case-by-case)
- Religious boundary: AI must refuse precept transmission, awakening
  certification, karmic diagnosis, spirit-medium framing, etc.
- Dual-track content license: code MIT, master content CC BY-NC-SA 4.0,
  prompts CC BY 4.0
- Takedown + appeal channel with 48h / 7d SLAs

**CHANGELOG.md** — Keep a Changelog format:
- [Unreleased] captures the current governance + community + npm work
- [0.3.0] retroactively documents the architectural rebuild (provenance,
  fidelity, NPX, multi-platform, HARD-GATE, two-stage review)
- [0.2.0], [0.1.0] historical sections

**CI fidelity smoke** — make HARD-GATE a real gate, not just documentation:
- New `fidelity-smoke` job runs one basic-difficulty fixture against one
  master per PR; picks the master touched by the diff, else rotates by
  day-of-year for uniform coverage
- Cost cap ≈ $0.05/PR (~10k-token system prompt × 1 request × Sonnet 4.6
  pricing). Forks without ANTHROPIC_API_KEY get an advisory pass so
  external PRs can still land
- `scripts/test-fidelity.py` gains `--max-tests N` flag; when capping, it
  sorts by difficulty (basic → intermediate → advanced) so smoke runs hit
  the reliable floor, not stress cases
- Old `fidelity` job renamed to `fidelity-full` (still workflow_dispatch)

README 声明 section now links to ETHICS.md so every reader sees the AI
disclosure and boundary rules before copying master content.

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

README.md

@@ -78,6 +78,8 @@
 
 本项目本着对佛教传统的尊重而建立。所有内容均依据佛教经典文献生成，不做教义评判，不代表任何宗派权威。生成内容仅供学习参考，如需正式修行指导，请亲近善知识。
 
+> **⚠️ 所有通过 Master-skill 生成的对话均为 AI 合成内容**，不代表历史上祖师的亲口开示、亲笔著作。项目遵守严格的版权分级与教界边界——详见 **[ETHICS.md](ETHICS.md)**（AI 透明度、版权 Tier A–D、禁止行为、内容双轨授权、紧急下架通道）。
+
 ---
 
 ## 特性