release: v0.3.6

[bug-ops]

Summary

• Bump version from 0.3.5 to 0.3.6
• Update CHANGELOG.md with release notes for v0.3.6

Changes since v0.3.5

• Bump rmcp from 1.3.0 to 1.4.0; remove now-redundant tool_router struct field (auto-generated by macro since 1.4.0)
• Bump tokio from 1.50.0 to 1.52.0
• Bump toml from 1.1.1 to 1.1.2
• CI: fix nightly rustfmt failures when component is temporarily unavailable (--allow-downgrade)

Checklist

• Version updated in all manifests
• CHANGELOG.md has release section with date
• README reflects new version (dynamic badges, no change needed)
• All CI checks pass locally (fmt, clippy, nextest 349 tests)
• Ready for tagging after merge