[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>

studio-v2/Dockerfile

@@ -4,13 +4,14 @@ FROM node:20-alpine AS builder
 WORKDIR /app
 
 # Copy package files
-COPY package.json package-lock.json* ./
+COPY studio-v2/package.json studio-v2/package-lock.json* ./
 
 # Install dependencies
 RUN npm install
 
-# Copy source files
-COPY . .
+# Copy source files + shared types
+COPY studio-v2/ .
+COPY shared/ /shared/
 
 # Build arguments for environment variables (needed at build time for Next.js)
 ARG NEXT_PUBLIC_VOICE_SERVICE_URL