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>

hooks/run-hook.cmd

@@ -0,0 +1,29 @@
+: ; # Polyglot wrapper — runs as cmd.exe on Windows, bash on Unix
+: ; exec bash "$0" "$@" 2>/dev/null
+: ; exit
+@echo off
+setlocal enabledelayedexpansion
+
+set "HOOK=%~1"
+set "HOOK_DIR=%~dp0"
+
+:: Try common Git for Windows bash locations
+for %%B in (
+    "C:\Program Files\Git\bin\bash.exe"
+    "C:\Program Files (x86)\Git\bin\bash.exe"
+    "%LOCALAPPDATA%\Programs\Git\bin\bash.exe"
+) do (
+    if exist %%B (
+        %%B "%HOOK_DIR%%HOOK%" %2 %3 %4 %5
+        exit /b %ERRORLEVEL%
+    )
+)
+
+:: Fallback: try bash from PATH
+where bash >nul 2>&1 && (
+    bash "%HOOK_DIR%%HOOK%" %2 %3 %4 %5
+    exit /b %ERRORLEVEL%
+)
+
+:: No bash found — exit silently
+exit /b 0