[interface-change] Phase 4: Extract shared types + fix Docker context

Shared types extracted to shared/types/:
- companion.ts (33+ types, was 100% duplicated admin-lehrer ↔ studio-v2)
- klausur.ts (18+ types, was 95% duplicated across 4 locations)
- ocr-labeling.ts (11 types, was 100% duplicated admin-lehrer ↔ website)

Original type files replaced with re-exports for backward compat.
tsconfig.json paths updated with @shared/* alias in all 3 services.

Docker: Changed build context from ./service to . (root) so shared/
is accessible. Dockerfiles updated to COPY service/ + shared/.

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

admin-lehrer/app/(admin)/education/klausur-korrektur/_components/types.ts

@@ -1,34 +1,11 @@
 /**
- * Local form types for Klausur-Korrektur page
+ * Local form types for Klausur-Korrektur page.
+ * Re-exported from the shared module.
  */
 
-export interface CreateKlausurForm {
-  title: string
-  subject: string
-  year: number
-  semester: string
-  modus: 'abitur' | 'vorabitur'
-}
-
-export interface VorabiturEHForm {
-  aufgabentyp: string
-  titel: string
-  text_titel: string
-  text_autor: string
-  aufgabenstellung: string
-}
-
-export interface EHTemplate {
-  aufgabentyp: string
-  name: string
-  description: string
-  category: string
-}
-
-export interface DirektuploadForm {
-  files: File[]
-  ehFile: File | null
-  ehText: string
-  aufgabentyp: string
-  klausurTitle: string
-}
+export type {
+  CreateKlausurForm,
+  VorabiturEHForm,
+  EHTemplate,
+  DirektuploadForm,
+} from '../../../../../../shared/types/klausur'