Implement package metadata, synchronized versioning, and release workflows #108

Summary

Implement the package metadata, synchronized version policy, release workflow,
and PyPI publishing workflow required by the PyPI release umbrella issue.

Scope

• Prepare motrix-env-core for public distribution.
• Prepare motrix-deploy for public distribution.
• Prepare motrix-rl for public distribution.
• Add package LICENSE files.
• Declare Apache-2.0 SPDX metadata and license files.
• Add Homepage, Repository, Issues, and Changelog URLs.
• Add keywords and PyPI classifiers.
• Add py.typed markers.
• Remove unused dependencies from published metadata.
• Change public package metadata to Requires-Python: >=3.10,<3.14.
• Pin every cross-workspace dependency to the shared workspace version.
• Add Commitizen configuration.
• Automate normal release version bump PRs.
• Automate main -> stable release PR creation.
• Automate stable tag and GitHub Release creation.
• Automate hotfix version bumps and hotfix/* -> stable PRs.
• Add PyPI publishing jobs in dependency order.
• Add workspace version and dependency-pin contract tests.
• Document the release and publishing workflows.

Version and dependency policy

Every workspace package must use the same version. Every dependency from one
workspace package to another must be an exact pin to that version:

"motrix-env-core==0.4.0b0"
"motrix-deploy==0.4.0b0"

The bump automation must update package versions, cross-workspace pins, and
uv.lock together.

Validation

• prek run --all-files passes.
• actionlint passes.
• uv lock --check passes.
• Workspace version contract tests pass.
• Commitizen auto predicts the expected next version.
• Commitizen beta predicts the next beta.
• A clean-worktree bump updates every package version.
• A clean-worktree bump updates every cross-workspace dependency pin.
• A clean-worktree bump refreshes every workspace version in uv.lock.
• All three sdists build successfully.
• All three wheels build successfully.
• Wheel metadata declares Requires-Python: >=3.10, <3.14.
• Wheel metadata declares the Apache-2.0 SPDX expression and license file.
• Wheels contain LICENSE and py.typed.
• Wheel metadata contains project URLs and Python 3.10–3.13 classifiers.
• Published cross-workspace dependencies are exactly pinned.
• Dependency resolution succeeds for Python 3.10–3.13 on Linux x86_64.
• Dependency resolution succeeds for Python 3.10–3.13 on macOS arm64.

Acceptance criteria

• The implementation PR is reviewed and merged.
• The package and workflow validation above passes.
• No public package retains an unpinned or ranged workspace dependency.
• The release workflow is ready for repository and publisher setup.