Rebuild Progress Agentic RAG plugin with E2E coverage and WordPress.org release pipeline

[ignatoffprogress]

This branch replaces the legacy procedural plugin with the new WordPress.org-ready progress-agentic-rag implementation. It adds a namespaced PHP architecture, admin settings/indexation UI, server-side Progress API integration, manual sync/delete/label reprocessing flows, and a front-page search widget that proxies requests through WordPress without exposing the service token.

It also adds full test/release tooling: Docker-based PHP lint/PHPUnit, Playwright E2E coverage for the external search widget CDN integration, release artifact checks, and GitHub Actions workflows for PR/main testing plus tag-only WordPress.org SVN deployment.

Major Changes

• New plugin bootstrap: progress-agentic-rag.php, src/*, templates/*, scoped assets.
• Removes old legacy entrypoint/includes from origin/main.
• Adds secure server-side proxy for widget traffic and token injection.
• Adds front-page widget rendering only when connection settings are complete/reachable.
• Adds PHPUnit coverage for settings/API/manual sync behavior.
• Adds Playwright tests for widget rendering, token secrecy, proxy behavior, edge cases, and responsive checks.
• Adds test-only E2E mu-plugin fixtures for deterministic upstream API stubbing.
• Adds GitHub Actions:
  • Tests: runs on develop-v2 and main pushes/PRs.
  • Deploy to WordPress.org SVN: dry-runs on PR/manual, deploys only on numeric tag pushes.
• Adds release metadata validation for plugin header version, constant, readme.txt stable tag, and changelog heading.

Review Focus

• Credential handling: token should never appear in DOM, browser storage, localized data, console, or browser request headers.
• Proxy security: method/path/header/query validation and redaction.
• Release behavior: BUILD_DIR contents, .distignore, metadata checker, and tag-only deploy guard.
• Backward compatibility: old nuclia_* options and sync-table compatibility are intentionally preserved.