perf-sentinel chart v0.2.0

Added

• Artifact Hub listing. The chart is now discoverable on artifacthub.io. charts/perf-sentinel/artifacthub-repo.yml documents the repository ownership and is pushed to the OCI registry under the special artifacthub.io tag on every release. Chart.yaml now carries artifacthub.io/* annotations (category, license, links, images).
• SPDX SBOM per release. Every chart release ships a Syft-generated SPDX SBOM as a GitHub Release asset, attested via actions/attest with the SBOM predicate and verifiable through gh attestation verify --predicate-type https://spdx.dev/Document/v2.3.

Changed

• docs/HELM-DEPLOYMENT.md (and its French parity) gains an Artifact Hub section, an SBOM verification subsection, and an OCI-based gh attestation verify oci://... recipe alongside the existing tarball-based one.