docs/ci: [#448] define release process and add release automation workflows

[josecelano]

Summary

• add release operational guide in docs/release-process.md
• extend and simplify container workflow to publish from main/develop/release branches
• add dedicated crate release workflow for SDK crate on releases/vX.Y.Z
• enforce SDK crate release metadata and add publish-crate badge in README
• add release-new-version skill for agent workflow guidance

Included changes

• docs/release-process.md (new)
• .github/workflows/container.yaml (updated)
• .github/workflows/publish-crate.yaml (new)
• packages/sdk/Cargo.toml (metadata for publish readiness)
• README.md (new workflow badge)
• .github/skills/dev/git-workflow/release-new-version/skill.md (new)
• AGENTS.md (skill registration)

Closes #448

[josecelano]

ACK 649a682