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>

.version-bump.json

@@ -0,0 +1,9 @@
+{
+  "files": [
+    {"path": "package.json", "field": "version"},
+    {"path": ".claude-plugin/plugin.json", "field": "version"},
+    {"path": ".claude-plugin/marketplace.json", "field": "plugins.0.version"},
+    {"path": ".cursor-plugin/plugin.json", "field": "version"},
+    {"path": "gemini-extension.json", "field": "version"}
+  ]
+}