ci: add nightly CLI release and Homebrew nightly formula update

[oscarcv]

Summary

Adds a new nightly delivery pipeline for the CLI and publishes a separate Homebrew nightly formula in oscarcv/tap.

What’s Included

• New workflow: .github/workflows/nightly.yml
• Triggered on:
  • merge/push to main
  • daily schedule (0 3 * * *)
  • manual dispatch
• Builds snapshot-report for macOS:
  • arm64
  • x86_64
• Packages and publishes assets to a moving prerelease tag:
  • tag: nightly
  • assets:
    • snapshot-report-nightly-macos-arm64.tar.gz
    • snapshot-report-nightly-macos-x86_64.tar.gz
    • matching .sha256 files
• Updates tap repo formula:
  • file: Formula/snapshot-report-nightly.rb
  • installs binary as snapshot-report-nightly (keeps stable and nightly side-by-side)
  • uses HOMEBREW_TAP_TOKEN for authenticated push to oscarcv/tap

Why

• Enables quick validation of unreleased CLI changes after merges.
• Provides a consistent nightly installation path for CI and early adopters.
• Avoids impacting stable Homebrew users by using a separate formula name.

Operational Notes

• Requires repository secret: HOMEBREW_TAP_TOKEN
• Workflow uses concurrency control (nightly-release) to avoid overlapping nightly publishes.
• Nightly version in formula is generated as: YYYY.MM.DD.<run_number>

Install (nightly)

brew tap oscarcv/tap
brew install snapshot-report-nightly
snapshot-report-nightly --help

Scope / Non-Goals

• CI/release automation only.
• No runtime code changes in CLI/library.
• Stable release workflow remains unchanged.