Restore cmd/devvault entrypoint so GoReleaser can build tagged releases

[Copilot]

The goreleaser release job failed because the configured build target (cmd/devvault) no longer existed in the repo, causing release artifact generation to abort for tag builds. This PR restores the expected CLI entrypoint and prevents it from being dropped by ignore rules.

• Root cause addressed: missing release build target

  • Reintroduced cmd/devvault/main.go as the CLI binary entrypoint.
  • Wired it back to the existing command execution path via internal/cli.

• Source tracking hardening

  • Updated root binary ignore patterns in .gitignore to be slash-anchored (/devvault, /devvault-demo, etc.) so only top-level built artifacts are ignored, while cmd/devvault/** remains trackable.

• Entrypoint shape

  package main
  
  import "devvault/internal/cli"
  
  func main() {
      cli.Execute()
  }

[Saravanakumar2602]

merged for copilot changes