feat: HA cluster with Raft consensus, GHCR publishing and Helm repo

[caikpigosso]

Summary

• HA Cluster v2.5.0: Raft consensus leader election, TCP state replication, automatic shard migration, DNS-based peer discovery, and collection sync across nodes
• CI/CD — GHCR: Replace DockerHub with GitHub Container Registry (zero secrets, uses GITHUB_TOKEN). Multi-arch images (amd64/arm64) with automatic semver tags via docker/metadata-action
• Helm chart repo: New workflow publishes the Helm chart to GitHub Pages via chart-releaser-action. Consumers can helm repo add directly from the repo

Key changes

• src/cluster/raft_node.rs — Raft consensus state machine (leader election, log replication, heartbeats)
• src/cluster/shard_migrator.rs — Automatic shard migration on node join/leave
• src/cluster/collection_sync.rs — Collection metadata sync across cluster
• src/replication/durable_log.rs — WAL-based durable replication log
• src/config/vectorizer.rs — Cluster configuration (DNS discovery, gRPC ports, timeouts)
• .github/workflows/release-artifacts.yml — GHCR push (replaced DockerHub)
• .github/workflows/helm-release.yml — Helm chart packaging and GitHub Pages index
• helm/vectorizer/ — StatefulSet support, headless service, GHCR image default

Test plan

• Verify release-artifacts.yml workflow passes on next release tag
• Verify Helm chart publishes to gh-pages branch
• helm repo add vectorizer https://hivellm.github.io/vectorizer works after first release
• docker pull ghcr.io/hivellm/vectorizer:latest works after first release
• Run scripts/test-local-cluster.sh for 3-node HA cluster validation
• Run cargo test cluster for unit/integration tests

🤖 Generated with Claude Code