polish: cleanup unused code, i18n gaps, a11y, error handling

- Removed unused ApproverMultiSelect imports (ArtefactDetailPanel, TranslationDetailPanel)
- Removed stale editProjectId/editCampaignId state from ArtefactDetailPanel
- Added 3 missing i18n keys (selectVersionFirst, pendingReviewInfo, noReviewInfo)
- Added error toast on link picker API failure (PostDetail)
- Added ARIA attributes to PortalSelect (role=combobox, aria-expanded, listbox, option)
- Deleted test screenshots from project root
- Simplified artefact creation modal: title + type only (removed brand/project/campaign/approver/description)
- Cleaned up ArtefactDetailPanel props (removed unused projects/campaigns)
- Translation submit-review: requires source_content before allowing review
- Artefact submit-review: requires at least one attachment for design/video
- Translation reviewer moved to Review tab (single select, mandatory)
- Server blocks translation submit without reviewer

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/src/pages/PostDetail.jsx

@@ -134,6 +134,7 @@ export default function PostDetail() {
       }
     } catch {
       setLinkCandidates([])
+      toast.error(t('common.error'))
     }
   }
 
@@ -468,8 +469,6 @@ export default function PostDetail() {
           onUpdate={loadComposition}
           onDelete={() => { setOpenArtefact(null); loadComposition() }}
           assignableUsers={teamMembers}
-          projects={[]}
-          campaigns={campaigns}
         />
       )}
     </div>