feat(with-watch): add public release automation

[kdy1]

Summary

• promote with-watch to a public release target by enabling crate publication and adding it to the cargo-mono publish-tag allowlist
• add a dedicated release-with-watch GitHub Actions workflow for signed multi-platform GitHub Releases and Homebrew tap updates
• document the new release contracts across AGENTS/docs and add a Homebrew formula template for with-watch

Testing

• cargo test -p with-watch
• cargo test --workspace --all-targets
• cargo publish -p with-watch --dry-run
• cargo mono publish --dry-run
• ./scripts/release/update-homebrew.sh --project with-watch --version 0.1.0 --darwin-amd64-url https://example.com/with-watch-darwin-amd64.tar.gz --darwin-amd64-sha256 1111111111111111111111111111111111111111111111111111111111111111 --darwin-arm64-url https://example.com/with-watch-darwin-arm64.tar.gz --darwin-arm64-sha256 2222222222222222222222222222222222222222222222222222222222222222 --linux-amd64-url https://example.com/with-watch-linux-amd64.tar.gz --linux-amd64-sha256 3333333333333333333333333333333333333333333333333333333333333333 --dry-run