fix: Restore all files lost during destructive rebase

A previous `git pull --rebase origin main` dropped 177 local commits,
losing 3400+ files across admin-v2, backend, studio-v2, website,
klausur-service, and many other services. The partial restore attempt
(660295e2) only recovered some files.

This commit restores all missing files from pre-rebase ref 98933f5e
while preserving post-rebase additions (night-scheduler, night-mode UI,
NightModeWidget dashboard integration).

Restored features include:
- AI Module Sidebar (FAB), OCR Labeling, OCR Compare
- GPU Dashboard, RAG Pipeline, Magic Help
- Klausur-Korrektur (8 files), Abitur-Archiv (5+ files)
- Companion, Zeugnisse-Crawler, Screen Flow
- Full backend, studio-v2, website, klausur-service
- All compliance SDKs, agent-core, voice-service
- CI/CD configs, documentation, scripts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

billing-service/Dockerfile

@@ -0,0 +1,40 @@
+# Build stage
+FROM golang:1.23-alpine AS builder
+
+WORKDIR /app
+
+# Install git for go mod download
+RUN apk add --no-cache git
+
+# Copy go mod files
+COPY go.mod go.sum* ./
+
+# Download dependencies
+RUN go mod download
+
+# Copy source code
+COPY . .
+
+# Build the application
+RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o billing-service ./cmd/server
+
+# Final stage
+FROM alpine:3.19
+
+WORKDIR /app
+
+# Install ca-certificates for HTTPS requests (Stripe API)
+RUN apk --no-cache add ca-certificates tzdata
+
+# Copy binary from builder
+COPY --from=builder /app/billing-service .
+
+# Expose port
+EXPOSE 8083
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+    CMD wget --no-verbose --tries=1 --spider http://localhost:8083/health || exit 1
+
+# Run the application
+CMD ["./billing-service"]