Add dependabot.yml

[jabenninghoff]

• add dependabot.yml
• pin GitHub actions
• bundle update
• URL maintenance

[Copilot]

Pull request overview

This PR introduces automated dependency management and maintenance updates for the site’s Ruby/Jekyll toolchain and external links.

Changes:

• Add Dependabot configuration for Bundler and GitHub Actions.
• Pin GitHub Actions workflow dependencies to commit SHAs.
• Update Ruby gems (Gemfile.lock) and maintain external URLs (posts + HTMLProofer ignore list), plus add local setup/cleanup scripts.

Reviewed changes

Copilot reviewed 9 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
clean.sh	Adds a cleanup helper for resetting local Ruby/Jekyll artifacts and lockfile.
bootstrap.sh	Adds a bootstrap helper to configure/install bundled gems (including CI group).
_posts/2012-10-25-appsec-usa-2012.md	Replaces dead link with archived URL.
_posts/2012-07-11-information-safety-basics.md	Replaces dead 1Password link with archived URL.
_posts/2012-06-06-linked-passwords.md	Replaces dead 1Password link with archived URL.
_posts/2011-11-17-appsec-usa-2011-video.md	Replaces dead AppSec USA links with archived URLs.
_posts/2011-09-26-bsm-presentation.md	Replaces dead AppSec USA links with archived URLs.
_posts/2011-09-21-appsec-usa-2011.md	Replaces dead AppSec USA links with archived URLs (including image link target).
Rakefile	Adds a URL to HTMLProofer’s ignore list.
Gemfile.lock	Updates gem versions via bundle update.
.github/workflows/ruby.yml	Pins action versions to commit SHAs.
.github/dependabot.yml	Adds weekly Dependabot updates for Bundler and GitHub Actions.

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