Add G5 repository-only pnpm distribution

[terrizoaguimor]

What changed

• define a machine-checked repository-only distribution policy for @pliegocss/cli
• build native CLI/LSP payloads for Windows x64, Linux x64 GNU, and macOS arm64
• assemble one universal, zero-dependency, no-lifecycle npm-format tarball installed with pnpm
• generate SHA-256 inventories, CycloneDX 1.5 SBOMs, and GitHub/Sigstore attestations
• fail closed on tag workflows unless immutable GitHub Releases are enabled
• document the consumer, release-authority, maturity, and RC.2 evidence boundaries

Why

G5 needs a convenient Node launcher without making npmjs a release authority. The supported path is an exact GitHub Release asset verified first and then installed locally with pnpm.

This PR is intentionally stacked on #3 and does not create a tag or Release.

Impact

• npmjs publication remains forbidden
• the 19 Rust crates remain one exact-version crates.io compatibility unit
• the optional Node package contains both native tools and performs no install-time download or script
• supported binary hosts are explicit; Authenticode and Apple notarization are not claimed

Validation

• pnpm check:repository-distribution
• pnpm check:attribution
• pnpm check:docs
• pnpm check:maturity
• pnpm check:release-authority
• pnpm check:release-contract
• pnpm install --frozen-lockfile
• actionlint on CI and distribution workflows
• real Windows release build and execution of both binaries
• real cargo-cyclonedx =0.5.9 generation and native staging

pnpm verify:fast passed through the new G5 gate, then the local Windows host blocked three pre-existing temporary pliego-css-agent test executables with Application Control error 4551. Hosted CI is the authority for that environment-specific remainder.

[terrizoaguimor]

G5 hosted evidence

Final exact source:

• commit: cffbdf868bc52d5708e750e989a9c147e578e4df
• Git tree: f37e5d1e533e424742ab6667340282d29c075b50
• worktree: clean and pushed

Hosted runs:

• exact-source push distribution: passed
• PR integration distribution: passed
• manual exact-source attestations: passed
• exact-source CI: passed
• PR integration CI: passed
• browser/output push and PR matrices: passed

Distribution proof:

• 3 native build/execute lanes passed
• one universal @pliegocss/cli tarball installed offline with pnpm 11.7.0 --ignore-scripts and executed on Windows x64, Linux x64, and macOS arm64
• 10 declared artifacts plus distribution manifest and SHA256SUMS
• package: pliegocss-pnpm-0.1.0-rc.2.tgz
• package SHA-256: 3bcc3e0bf0c925d090b1a96f7864e1ab0e3ed1cfede21c8ea2b5971928c4aee9
• package bytes: 23087327
• external gh attestation verify: all 12 release files matched SLSA v1 provenance for the exact SHA
• external gh attestation verify --predicate-type https://cyclonedx.org/bom: all 6 native binaries matched CycloneDX 1.5 SBOM attestations for the exact SHA

No tag or GitHub Release was created. npmjs publication remains forbidden. Repository Immutable Releases are currently disabled, so the tag path remains fail-closed until Mario explicitly authorizes enabling that repository setting. RC.2 is not retroactively promoted by this branch evidence.