feat: add multi-platform plugin support and session-start hook

Add support for 5 platforms beyond NPX:

- Claude Code: .claude-plugin/plugin.json + marketplace.json
- Cursor: .cursor-plugin/plugin.json + hooks-cursor.json
- Codex CLI: .codex/INSTALL.md with symlink setup
- OpenCode: .opencode/INSTALL.md with plugin config
- Gemini CLI: gemini-extension.json + GEMINI.md

Infrastructure:
- SessionStart hook with platform detection (Claude Code,
  Cursor, Copilot CLI) that injects available masters list
- Cross-platform run-hook.cmd polyglot wrapper (Windows + Unix)
- .version-bump.json for unified version management across
  all platform config files
- Update README/README_EN with multi-platform install instructions

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

package.json

@@ -1,6 +1,7 @@
 {
   "name": "master-skill",
   "version": "0.3.0",
+  "type": "module",
   "description": "Chinese Buddhist Master AI Skills — RAG-grounded, source-cited, fidelity-tested",
   "bin": {
     "master-skill": "./bin/cli.mjs"
@@ -8,5 +9,5 @@
   "keywords": ["claude-skills", "agent-skills", "buddhism", "ai-persona", "rag", "digital-humanities"],
   "license": "MIT",
   "repository": {"type": "git", "url": "https://github.com/xr843/Master-skill"},
-  "files": ["bin/", "prebuilt/", "scripts/"]
+  "files": ["bin/", "prebuilt/", "scripts/", "hooks/", ".claude-plugin/", ".cursor-plugin/", ".codex/", ".opencode/"]
 }