refactor: rename mstsconv command to msconv for shorter CLI usage

- Rename cmd/mstsconv.go to cmd/msconv.go
- Update command name from mstsconv to msconv in all references
- Update documentation in README.md and CLAUDE.md

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Co-Authored-By: Claude <noreply@anthropic.com>

refactor: replace /run with direct command execution

Replace the /run command system with intuitive direct execution:
- /command args: executes directly, stays in current mode
- /command: switches to command mode (unchanged behavior)

Benefits:
- More natural syntax (/uuid 5 vs /run uuid 5)
- Fewer keystrokes for quick operations
- Better workflow for contextual commands
- Perfect for JWT workflow: see timestamp → /ts2date 1516239022

Changes:
- Removed /run command infrastructure from shell
- Implemented smart execution logic in execCommand()
- Updated documentation with real-world examples
- Added README example showing JWT → timestamp conversion workflow

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Co-Authored-By: Claude <noreply@anthropic.com>

feat: add /run command for direct execution in interactive shell

Add new /run command that allows executing any command directly without
switching modes in the interactive shell. Features include:

- Direct command execution with syntax: /run <command> [args...]
- Auto-completion support for command names after /run
- Help display when used without arguments
- Error handling for unknown commands

Updated CLAUDE.md documentation to include:
- Shell system capabilities with /run command
- Dedicated /run command section with usage examples
- Updated built-in commands list

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>