Restore missing cmd/devvault entrypoint to unblock macOS CI Build & Test

[Copilot]

Build & Test (macos-latest) failed because the e2e test builds ../cmd/devvault, but that package path was absent from the repository. This PR restores the expected CLI entrypoint and adjusts ignore rules so the source path is tracked.

• Root cause

  • test/e2e_test.go invokes:

    go build -o <temp-bin> ../cmd/devvault

  • Repository only had cmd/devvault-demo, so the build target did not exist.

• Code change: restore canonical CLI package path

  • Added cmd/devvault/main.go as the executable entrypoint.
  • Entrypoint delegates to existing command wiring in internal/cli.

• Repo hygiene: narrow binary ignore scope

  • Updated .gitignore from broad devvault / devvault.exe patterns to root-anchored /devvault / /devvault.exe.
  • Keeps root-level built binaries ignored while allowing cmd/devvault/ source files to be tracked.

• Entrypoint snippet

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