Add Platform Version 2026.3 packages list and combined release notes

[jcPimcore]

Summary

• Adds the Platform Version 2026.3 packages list (doc/02_Pimcore_Platform/04_Platform_Versions/01_2026.3.md), including the new pimcore/portal-ui-kit (Enterprise) package, and renumbers the 14 existing entries plus the README.md table row.
• Expands the combined release notes (doc/02_Pimcore_Platform/05_Updating_Pimcore/02_Release_Notes/01_2026.3.md) from the existing minimal Quill Bundle deprecation note into full release notes: Generic Data Index performance/stability/traceability, the Portal Engine rework and new portal-ui-kit, experimental Pimcore Embeddings, telemetry extension, Agent Bundle (beta) updates, plus per-bundle additional changes and upgrade notes links.

Test plan

• Review the packages list against composer.json's conflict section on this branch
• Review the combined release notes for accuracy and tone
• Confirm README.md links resolve correctly once merged

🤖 Generated with Claude Code

[fashxp]

more required changes:

What's wrong

1. Embeddings is understated.
   • It says third-party providers come "in the future", but EmbeddingProviderInterface is public now, so custom
     providers work today.
   • It also covers asset documents (#758), not just images.
   • Semantic search sits behind a new permission, bptb_semantic_search_permission.
   • It doesn't say that this needs Enterprise (Backend Power Tools) or how customers get the inference service.
2. Quill:
   • The link points to the 2026.x branch; every other link uses 2026.3.
   • The replacement, pimcore/pimcore-wysiwyg-editor, isn't mentioned, even though the bundle's own upgrade note
     names it.
   • The bundle is now marked abandoned, so composer will warn.
   • The replacement isn't in the platform package list either.

Missing: upgrade-critical

• The legacy Portal frontend is deprecated and will be removed in 2027.1. New portals now default to the Studio
  frontend (#993); existing portals are left as they are.
• Renderlet parameters passed as request attributes are deprecated, and Asset::correctPath() now renames .html/.js uploads.
• Elasticsearch ≥ 8.12.2 applies to the whole platform (via elasticsearch-client ^2026.3). State it once under General, not per bundle.

Missing: features that deserve more space

• OAuth 2.1 authorization server in Studio Backend: opt-in, with PKCE and a consent screen in Studio UI. OAuth
  tokens are also accepted on the Simple REST and MCP endpoints (#1958, #2028, #3951, #356).
• The Simple REST MCP server is no longer experimental (#362), plus about 10 MCP quality PRs.
• Notification subscriptions with email delivery and a preferences screen (#1959, #3913).
• Studio UI:
  • accessibility: WCAG AA contrast, focus-visible, skip link, focus restore
  • draggable modals and a resizable, pinnable sidebar
  • batch edit across several languages at once
  • configurable page sizes
  • version co-authors, and Properties in version view
  • user owner/modification columns and filters, plus an asset size filter
  • inline upload in the relation editable, and creating an object from the relation toolbar
• Dutch and Polish translations across Studio and about 25 bundles.
• Core:
  • faster saving of localized fields (#19375, #19369; closes the long-standing #11757)
  • less thumbnail I/O
  • configurable thumbnail cache lifetime
  • per-extension MIME type overrides
  • custom HTML sanitizer
  • arguments for Calculated Value calculators
  • workflow custom_extensions
  • NoteEvents::POST_DELETE
• Symfony 8 readiness across about 20 bundles.

[jcPimcore]

done by commit 2df8113

[jdreesen]

Which upcoming Symfony 8 release do you mean? Symfony 8.2?
Because Symfony 8 itself has been released almost a year ago 🤔