Modernize AgentFence repository presentation and documentation

[Adulph3]

Summary

• rebuild the README as a concise, security-focused landing page for the published v0.2.0 release
• document supported adapters, detector areas, trust boundaries, report semantics, CLI options, exit codes, installation choices, architecture, integrity verification, limitations, and FAQ
• refresh SECURITY.md, CONTRIBUTING.md, release/compatibility status, and project progress
• add focused bug, feature-request, and pull-request templates with secret-handling guidance

Scope

Documentation and GitHub repository presentation only. No production source, CLI behavior, package metadata, release tag, npm publication, or AGENTS.md changes.

Validation

• git diff --check
• issue-template YAML parsing
• Markdown structure and local-link validation
• npm run check:boundaries
• npm pack --dry-run --ignore-scripts (152 files)
• remote compare: 1 commit, 10 expected documentation/community files, 0 commits behind main

Hosted CI and CodeQL should provide the full repository gates for this PR.