VITEC headless v14: 5-bug fix unifies plugin renderers + cleanup

Resolves a cascade of TYPO3 v14 breaking changes that left every VITEC
plugin's JSON output silently empty:

1. `list_type` column dropped — all renderer page-discovery queries now
   filter by `CType = 'vitec_X'`.
2. `#[AsAllowedCallable]` attribute added to every public render() —
   without it v14 throws AllowedCallableException, which headless
   silently filters via its "Oops, an error occurred!" guard.
3. `$GLOBALS['TSFE']->id` is null inside JSON cObj context — page id
   now read from the `frontend.page.information` request attribute
   (TSFE fallback kept for legacy entry points).
4. page.tsconfig wizard items migrated to `CType = vitec_X` directly
   (legacy `CType=list, list_type=...` no longer exists in v14).
5. ContainerChildrenProcessor + ContentElementResolver dispatch the
   PLUGIN_RENDERERS map by CType (primary) with list_type fallback.

Beyond the bug fix this commit also contains:
- Datasheets renderer rewritten to "products with newest datasheet"
  semantics (filtered via Download.hideondatasheets).
- New vitec/card content block — multi-purpose card with backend
  preview and layout/background/aspect/alignment/border/shadow options.
- New vitec_container CType (b13 single-column container, FlexForm
  cssClass propagated into the JSON envelope).
- ContentElementResolver service for contentelement/contentelementcta
  link resolution; ContainerChildrenProcessor for nested plugin
  resolution inside b13 containers.
- Vitecset setup.typoscript: ContentElement import moved to top so
  lib.contentElement is defined before VITEC's tt_content blocks.
- Cleanup: 98 .bak.<timestamp> debugging backups removed; *.bak.* and
  /public/_assets_install/ added to .gitignore.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

public/_frontend/assets/index-Dsu1vSvE.css

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