Build installable plugin releases

[matthewdorman]

Summary

• integrate the read-only Plugin Reviewer runtime into the current repository
• add an explicit-allowlist build that produces plugin-reviewer.zip
• validate archive structure, runtime contents, PHP syntax, and version alignment
• add a least-privilege GitHub Actions workflow for PR/main validation and tagged GitHub Releases
• rewrite the README around a prominent installable-ZIP link and nontechnical wp-admin installation, audit, export, privacy, troubleshooting, and uninstall guidance
• preserve the anonymized dataset, dashboard, and Python generators as contributor/reference material while excluding them from releases

Release model

• main remains the stable, complete source branch
• development uses short-lived feature branches and pull requests
• version tags matching the plugin header (for example v0.1.0) create a deliberate plugin-reviewer.zip GitHub Release asset
• build jobs have read-only repository access; only the tag-gated publish job receives contents: write
• the ZIP includes only runtime plugin files and does not include Python, data, dashboard, tests, scripts, or repository configuration

Validation

• PHP lint: 9/9 runtime PHP files clean
• release build completed successfully
• ZIP validator passed required-file, top-level-directory, development-file exclusion, PHP lint, and plugin/readme version checks
• archive listing confirmed a single plugin-reviewer/ top-level directory
• GitHub Actions workflow YAML parsed successfully
• git diff --check clean
• local branch and pushed remote SHA match

Closes #2