IONOS(assistant): update submodule to v3.5.0 IONOS fork (NC33, major) (NSW-1073)

[printminion-co]

Summary

Major fork bump split out of #381 so it can be tested and reverted on its own: apps-external/assistant from IONOS fork v2.12.0-6152a89 (upstream v2.12.0) to upstream v3.5.0 (NC 33–34) + IONOS delta, from IONOS-Productivity/nc-assistant#5.

Fork PR	IONOS-Productivity/nc-assistant#5 → ionos-dev-v33 (= vanilla v3.5.0)
Pinned here	PR head f23d180 (pre-tag)
Final pin	prerelease tag v3.5.0-<sha7> after the fork PR merges

IONOS delta on v3.5.0

• numberOfImages hide (filteredShape in TaskTypeFields.vue): kept; v3 still renders task inputs through TaskTypeFields
• NSW-1017 mimetype detection fix for task output files (4 commits from IONOS(assistant): fix mimetype detection for task output files (NSW-1017) nc-assistant#4): folded in, so the NC33 line carries it; add build workflow #4 can be closed after merge

Validation so far

• Fork CI: php-cs, openapi, reuse, phpunit stable33/34 pass; psalm / eslint / node never start in the fork (runner label), run locally instead: psalm (OCP stable33 + stable34), npm run lint, npm run build all clean
• Artifact build with this pin: green (built in the combined evaluation run on IONOS: upgrade fork app submodules to max NC33-compatible upstream (NSW-1069) #381)

Needs testing (v2 → v3)

• Assistant opens; text, image and other task types run end to end
• Image generation form does not show "number of images"
• Task output files download with the correct mime type and file extension (NSW-1017)
• Assistant entry points in Files / Text / Talk still work
• run .dev/container/check_release.sh pr-382 ncw — validate pr locally
• after the fork PR merges: re-point the gitlink to the prerelease tag

Related: #381 (rest of the fork sweep). Jira: NSW-1073 (sub-task of NSW-1069)