docs: complete v0.1.2 release metadata

[ludioo]

Summary

Completes the remaining v0.1.2 release metadata after the successful EditMode CI rollout.

Changes

• Update package version to 0.1.2
• Add the v0.1.2 changelog entry
• Document automated CI in the contributor guide
• Record the completed CI milestone in the roadmap

Scope

• Documentation and package metadata only
• No production source changes
• No workflow changes
• No credentials or secrets

Validation

• EditMode CI has completed successfully
• Unity version remains 2022.3.23f1
• Package, changelog, and roadmap versions are consistent