chore: unified release workflow with docker build

[tooandy]

Summary

• Replace release-please + docker-publish dual workflows with a single publish.yml workflow
• Manual trigger via workflow_dispatch with optional version input
• Auto-increment patch version or specify custom version
• Generates changelog from commits
• Updates pyproject.toml + CHANGELOG.md, commits and tags
• Triggers Docker multi-platform build on tag push
• Creates GitHub Release with Docker image URLs in body

Workflow

workflow_dispatch → update version + changelog → git commit + tag → docker build → release

Test plan

• Merge this PR
• Run "Publish Release" workflow manually from Actions tab
• Verify: version bumped, changelog updated, tag created, docker built, release published with image URLs