The `pdf_tools_url` claim makes the UI show a "PDF tools" button that embeds a
self-hosted Stirling-PDF (or any web PDF toolkit) for merge/split/OCR/convert — the
same BYO-embed pattern as terminal_pty_url, so FluxFiles rides the free OSS instead of
building a competitor.

- Claims::$pdfToolsUrl, http(s)-only (non-http schemes dropped on decode).
- Pure UI: a sandboxed iframe + no new server endpoint → works in every mode (incl. the
  Laravel/WordPress proxy adapters), no added attack surface.
- fm.js getter + openPdfTools()/closePdfTools() + a toolbar button (x-show=pdfToolsUrl)
  + a modal in index.html. i18n pdf.title ×16.
- Forwarded by embed/node(+dist)/laravel/wordpress. docs/CONFIG.md. node 0.1.22.
- Test: pdf_tools_url forward + http/s-only in test-tenant-config; Playwright-verified
  the button/getter/modal/iframe embed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>