chore: gitignore agent scaffolding + local recon scratch

[UNC1739]

Summary

Hardens .gitignore so the artifacts that were accidentally committed to dev can't recur. Follows the just-completed history scrub of .feature-development/ from dev and 21 branches.

New ignore rules (added beside the existing .claude/ entry):

• .feature-development/ — AI feature-workflow scaffolding (design notes, plans, reviews). This is the directory that leaked; it's internal/local-only and never belongs in the repo.
• /demos/ — root-anchored local scratch demos. Deliberately anchored so it does not touch the tracked examples/ or testdata/demo/ dirs.
• *-users.txt — operator recon output (e.g. fox-users.txt, km-users.txt) — engagement-specific target/user lists that shouldn't be public.

Verification

git check-ignore confirms the new patterns match .feature-development/plan.md, demos/x.txt, fox-users.txt, km-users.txt, while examples/enum-custom-demo/main.go and testdata/demo/Dockerfile.ssh remain tracked (not ignored). No currently-tracked file matches any new pattern.

Targeting dev (the active integration branch where the leak occurred); it reaches main via #214.

🤖 Generated with Claude Code

[github-actions]

Gemini review skipped — non-code PR (only changed files matching docs/**, .claude-plugin/**, *.md, *.txt, images, or license-like files). Post @gemini on a review comment to force a review.

[github-actions]

Codex review skipped — non-code PR (only changed files matching docs/**, .claude-plugin/**, *.md, *.txt, images, or license-like files). Post @codex on a review comment to force a review.

[github-actions]

Claude review skipped — non-code PR (only changed files matching docs/**, .claude-plugin/**, *.md, *.txt, images, or license-like files). Post @claude on a review comment to force a review.