docs: complete MVP command reference and troubleshooting

[dDevAhmed]

Summary

Implements CLI-035 by bringing the public CLI documentation in sync with the implemented MVP command behavior.

Included

• expands the command reference for every implemented MVP command
• documents arguments, options, examples, configuration, and exit behavior
• documents supported new templates and generator safety
• documents doctor, dev, test, and Testnet deployment behavior
• adds a dedicated troubleshooting guide for setup/config/process/network failures
• refreshes Quick Start with real implemented workflows
• removes stale foundation-stage installation guidance
• updates README command status from Planned to Implemented
• clearly marks Mainnet deploy, stellarforge add, plugins, and remote templates as unavailable
• cross-links installation, configuration, exit codes, security, and troubleshooting

Security

• raw secret/signing material is explicitly excluded from examples
• troubleshooting guidance avoids environment/credential dumps
• Testnet-only deployment restrictions are stated consistently
• unsupported behavior is not presented as available

Closes #38