Release Jo 0.13.0

[liufengyun]

Release Jo 0.13.0

Summary

Cuts the 0.13.0 release. Release-metadata only, no compiler or library code is
touched. A minor bump rather than a patch because the release is
source-breaking: optional context parameters are dropped (#95, JIP-0002)
and IO.stdin is removed (#100).

What has changed

• stack-lang/tool/JoVersion.scala — version bumped to 0.13.0, verified with
  bin/jo.dev --version
• README.md — release badge and tag link updated to v0.13.0
• CHANGELOG.md — 0.13.0 section covering #94, #95 and #100, with the
  security and compatibility sections
• docs/public/versions.jsonl — entry appended for v0.13.0

Checklist

• Added / updated tests under tests/pos/ or tests/warn/ — release metadata only
• Docs updated if the change affects user-visible behavior
• All commits are signed off (why?)

Security impact

No change in this PR. The release itself carries two security-relevant changes,
both recorded in the changelog:

• Dropping optional context parameters closes a capability hole. A default
  satisfied a requirement silently, so allow none in e denied e only the
  ambient context that lacked a default rather than all of it. (#95)
• --source-root keeps absolute filesystem paths out of .sast files and
  generated documentation. (#94)

Compatibility impact

No change in this PR. The release is source-breaking, as recorded in the
changelog. The boxes below describe the 0.13.0 release as a whole, and match
what #95 and #100 reported when they merged.

• Source compatibility: existing code continue to compile — optional context parameter declarations and uses of IO.stdin no longer compile
• SAST compatibility
  • forward compatibility: new libraries can be used by old compiler
  • backward comopatibility: old libraries can be used by new compiler — libraries must be recompiled if they use optional context parameters
• Standard Library compatibility:
  • forward compatibility: new code can work with old stdlib
  • backward compatibility: old code work with the new stdlib — IO.stdin is removed
• Runtime Library compatibility:
  • forward compatibility: new code can work with old runtime
  • backward compatibility: old code work with the new runtime
• Build tool
  • Build spec compatibility: old projects continue to build
  • Joy package compatibility: old .joy can be consumed by new build tool