M6.1: Implement demo script

[bjcorder]

Labels: type:infrastructure, area:build, priority:high,
status:blocked, milestone:M6, phase:10

Summary

Create an end-to-end demo script that exercises the full ForkGuard
pipeline against synthetic fixtures.

Acceptance criteria

• scripts/demo.sh (bash) performs:
  1. Optionally wipe ~/.forkguard/ (confirmation prompt unless --yes)
  2. Invoke make fixtures to ensure fixtures exist
  3. Write a temporary forks.yaml pointing at fixture forks
  4. Load synthetic advisory directly into the DB
  5. Run forkguard scan against all four forks
  6. Render JSON, SARIF, and table reports
  7. Print a summary showing all four expected statuses appear
• Makefile has a demo target invoking the script with --yes
• Script exits non-zero if any expected status is missing

Dependencies

Depends on: #28, #22

Verification

make clean && make build && make demo

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