refactor: rename Buddha-skill → Master-skill

Matches internal architecture (create-master, master_xuanzang, etc.)
and accurately reflects content (historical Chinese Buddhist masters,
not the Buddha himself).

Changes:
- 32 text references across 9 files updated
- Sanskrit terms (buddha-dhātu, buddhatā) preserved in dictionary context
- GitHub repo renamed (preserves stars/forks/history, auto-redirects)
- Internal naming already uses master_* (unchanged)

All 79 tests pass.

tests/conftest.py

@@ -1,4 +1,4 @@
-"""Shared pytest fixtures for Buddha-skill tests."""
+"""Shared pytest fixtures for Master-skill tests."""
 
 import sys
 import os