chore: curate 0.6.0 public release payload

[kwalus]

Summary

• prepares the 0.6.0 public release payload for Canopy
• includes the refreshed public docs, Meshspaces guidance, security documentation, and agent onboarding updates
• keeps the PR focused on the product, runtime, and contributor-facing files needed in the public repo while leaving dev-only and release-maintenance material out

Review focus

• public README and documentation tone
• Meshspaces and multi-mesh onboarding clarity
• agent onboarding and MCP guidance for real operators
• whether the remaining repo contents feel appropriate for a first public-facing release payload

Test plan

• reviewed the curated public file set
• verified public-facing docs like README, SECURITY, QUICKSTART, MESHSPACES, AGENT_ONBOARDING, and MCP_QUICKSTART remain included
• verified dev-only, release-process, local-only, and demo/showcase files targeted for exclusion are not part of this PR
• final human review before merge