Snagify 0.5.0

Changelog

• 8bfaefe Add GitHub Action + Docker image (F1, F4)
• 65abfee Add credential-free protocol probes for Postgres/MySQL/Redis (F2)
• fcff552 Add custom shell checks in .snagify.yaml (F3)
• 314bcf4 Add plugin system with subprocess + JSON-RPC v1 contract (F6)
• 7d23638 Add secret / .env safety scanner (F5)
• e37a3b6 Fix npm bin path
• e885320 Fix release pipeline: drop goreleaser dockers block, build docker in its own job
• 6eb2b2c Revert Dockerfile to multi-stage go build (skip tarball fetch)
• 5285eee fixup! Add GitHub Action + Docker image (F1, F4)
• 5f2db31 fixup! Add GitHub Action + Docker image (F1, F4)
• fe0c34b fixup! Add GitHub Action + Docker image (F1, F4)
• f4068bf fixup! Add GitHub Action + Docker image (F1, F4)
• 828eb9e v0.5.0: bump version, update CHANGELOG and README install matrix