Checkpoint: headless JSON architecture documented + cleanup (Stufe 1+2)

Restore point before Stufe 3 (central resolver-service refactoring).

Includes this session's work:
- Success Story (usecase) rebuild: new fields/tabs, UsecaseSerializer,
  thin List/Show renderers, MM relations, inline content elements.
- vitec_columns content block (two-column layout with per-item content)
  incl. unified header section; special-cased JSON resolution.
- Container per-column flex (items[].config align/justify) + gap on parent.
- Unified header section across CEs/plugins/containers; header fields in JSON.
- ISO-style architecture spec: Documentation/Headless-JSON-Architecture.md.
- Cleanup: removed local scratch + verified .bak backups.
- Fixes: B-6 (undefined thumbnail variable in Downloadcardcollection image
  resolver), B-7 (unsatisfiable legacy CType OR branch in Downloadcard/Datasheets).

Rollback: git reset --hard snapshot-2026-07-09-pre-stufe3

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

public/_frontend/assets/vitec_usecaseshow-B8AiH3X6.js

@@ -0,0 +1 @@
+import{C as e,D as t,O as n,Z as r,b as i,k as a,n as o,w as s}from"./index-7LYai_r-.js";var c=r();function l({element:r,className:l,nested:u,devInfoTags:d,uid:f,spaceBefore:p,spaceAfter:m}){let h=r.data?.usecase?.usecase,g=r.appearance?.frameClass?.split(`,`).map(e=>e.trim()).includes(`vitec-full-width`)??!1,_=h?.caseimage?.publicUrl,v=h?.logoimage?.publicUrl;return(0,c.jsx)(o,{className:l,devInfoTags:d,fullWidth:g,nested:u,uid:f,spaceBefore:p,spaceAfter:m,children:(0,c.jsx)(`div`,{className:`vitec_usecaseshow__inner`,children:(0,c.jsxs)(s,{container:!0,spacing:3,alignItems:`start`,children:[_&&(0,c.jsx)(s,{size:{xs:12,md:5},children:(0,c.jsx)(t,{component:`img`,src:_,alt:h?.title??`Use case`,sx:{width:`100%`,height:`auto`,display:`block`,borderRadius:3}})}),(0,c.jsx)(s,{size:{xs:12,md:_?7:12},children:(0,c.jsxs)(e,{spacing:2,children:[v&&(0,c.jsx)(t,{component:`img`,src:v,alt:`${h?.title??`Use case`} logo`,sx:{height:48,width:`auto`,objectFit:`contain`,display:`block`}}),(0,c.jsx)(a,{variant:`overline`,color:`text.secondary`,children:`Success Story`}),h?.title&&(0,c.jsx)(a,{variant:`h4`,children:h.title}),h?.subtitle&&(0,c.jsx)(a,{variant:`subtitle1`,color:`text.secondary`,children:h.subtitle}),h?.teaser&&(0,c.jsx)(a,{variant:`body1`,sx:{fontStyle:`italic`},children:h.teaser}),h?.description&&(0,c.jsx)(t,{sx:i,dangerouslySetInnerHTML:{__html:h.description}}),h?.categories&&h.categories.length>0&&(0,c.jsx)(e,{direction:`row`,spacing:.75,flexWrap:`wrap`,useFlexGap:!0,children:h.categories.map(e=>(0,c.jsx)(n,{label:e.title??`Category`,size:`small`},e.uid??e.title))})]})})]})})})}export{l as VitecUsecaseShow};