refactor(web): rebuild web-embed-pdf on @simplepdf/embed, WebMCP on by default, PDF links in any case

[bendersej]

Background

@simplepdf/web-embed-pdf is loaded unpinned from unpkg by customer sites, so a publish reaches every site at once. It re-implemented what @simplepdf/embed already owns: the editor URL, loading the document (host fetch, then the ?open fallback) and the postMessage bridge. This PR rebuilds it on createEmbed. window.simplePDF, the script-tag attributes and the modal stay unchanged.

Changes

• The editor URL, document loading and the bridge come from createEmbed; the modal markup and CSS are kept byte for byte.
• WebMCP, on by default: while the editor is open, an in-browser agent on the page finds the editor's tools. webmcp="false" or setConfig({ webMCP: { enabled: false } }) turns it off. Every call goes through the editor's usual permissions.
• PDF links open in SimplePDF whatever the extension case, query string or fragment (Consent.PDF, form.pdf?ver=2, guide.pdf#page=3); links already detected keep opening.
• One shared fixture of link cases (web/src/__tests__/fixtures/pdf-link-cases.json) drives the unit test.
• Japanese and Dutch pages get their editor language.
• A SimplePDF /documents/<id> link opens the stored document directly.
• A companyIdentifier that cannot form an editor address (a URL, spaces, dots, underscores) logs an error and opens nothing. An identifier with no account behind it opens the editor, which shows its own error page.
• Every href 1.8.4 accepted still works (relative, data:, blob:), and so does an uppercase companyIdentifier.
• The build stays a single UMD file (the Chrome extension evaluates dist/index.js).
• One minor changeset (1.9.0).

Notes

• A browser test suite (in the internal repo) was written first against the published 1.8.4, then passed unchanged on this rewrite. Every assertion is proven by a deliberate regression that fails it.
• Bundle: 10.5 KB → 35.6 KB minified, 4.1 → 11.7 KB gzip (the core, including its WebMCP module, which UMD cannot split out).
• Size cap: web adds none. It inherits the 50 MB host-fetch cap every published @simplepdf/embed already ships (React 1.11+ has it today); above it, the document goes to the editor by URL.