release: prepare Emulsify Drupal 7.1.0

[callinmullaney]

This PR does the following:

• Prepares the Emulsify Drupal 7.1.0 release with updated release notes, upgrade guidance, README documentation, and release-readiness documentation.
• Expands release-readiness checks for Composer metadata, npm install/audit policy, PHP linting, documented npm commands, region rendering, favicon behavior, starterkit expectations, and semantic-release workflow coverage.
• Adds CI coverage for release readiness, scheduled/manual starterkit Storybook and accessibility checks, generated child-theme frontend tests, and favicon smoke testing with GD and Imagick.
• Fixes declared content_top and content_bottom regions so they render in both the parent theme and generated whisk child themes.
• Improves favicon package safety and diagnostics by validating managed package paths, reporting missing runtime dependencies, persisting sanitized SVG sources, and hardening SVG sanitization against CSS-based vectors.
• Clarifies that whisk is a generation-only starterkit source and removes default design-token pipeline assumptions from generated child-theme scripts.

Related Issue(s)

• N/A

Notes:

• This PR is intended to support a backward-compatible 7.x minor release.
• The release notes draft documents that Semantic Release should produce 7.1.0 only if a legitimate feat: commit remains in the final commit history after 7.0.0.
• License metadata still needs maintainer review before release: npm-side metadata now uses GPL-3.0-only, while Composer/Drupal.org metadata remains GPL-2.0-only.

Functional Testing:

• Run composer validate --no-check-publish.
• Run npm ci --ignore-scripts.
• Run npm audit --omit=dev.
• Run npm audit.
• Run npm run lint:php.
• Run npm run docs:check-commands.
• Run npm run release:check -- --skip-smoke.
• Run npm run release:check in an environment with GD and Imagick available.
• Generate a child theme from whisk, then run npm install, npm run build, npm run storybook-build, and npm run test from the generated child theme directory.
• Verify blocks placed in header, content_top, content, content_bottom, and footer render in the parent theme and generated child theme smoke output.
• Verify favicon package generation still works from the theme settings form or drush emulsify_tools:favicon-generate [theme_name].

[github-actions]

🎉 This PR is included in version 7.1.0 🎉

The release is available on GitHub release

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