Document why OpenCode Remote exists

[crankshift]

Summary

Add a README section explaining why OpenCode Remote exists and how it differs from broader remote-agent projects.

Context

The README should help users understand the narrower local-first gateway approach. It should compare OpenCode Remote with richer projects such as Hermes and OpenClaw while explaining the isolation tradeoff of agent-owned source or runtime folders.

Acceptance Criteria

• README explains why OpenCode Remote exists in one clear section.
• The section compares the project with richer remote-agent projects such as Hermes and OpenClaw.
• The section acknowledges those tools may offer broader functionality.
• The section explains the isolation tradeoff around agent-owned .hermes/ or .openclaw/ folders.
• The section positions OpenCode Remote as a narrower isolated CLI around normal OpenCode project workflows.
• The section mentions preserving project-folder workflows and inheriting OpenCode global and project-local skills without shipping a noisy default skill set.

Notes

Keep the tone factual and avoid claiming planned features are already shipped.