perf: build frontend once on runner instead of in Docker

- [x] Remove Docker compilation from server, scanner, migrate Dockerfiles
- [x] Use pre-built binaries injected by GoReleaser instead
- [x] Delete separate gateway container and merge into frontend
- [x] Update .goreleaser.yaml to reference pre-built binaries
- [x] Simplify Kubernetes deployment to remove gateway service
- [x] Simplify docker-compose to remove gateway container
- [x] Add backend proxy configuration to frontend

Dockerfile.migrate

@@ -1,47 +1,7 @@
 # Migration Engine - Database Migration Tool
-# Multi-stage build to compile with CGO support
+# This Dockerfile expects a PRE-BUILT binary from GoReleaser (no compilation)
+# GoReleaser injects the platform-specific binary automatically
 
-# Build stage
-# Let buildx handle platform automatically
-FROM golang:1.25-alpine AS builder
-
-# Get build platform from buildx
-ARG TARGETPLATFORM
-ARG TARGETOS
-ARG TARGETARCH
-
-# Install build dependencies for CGO
-RUN apk add --no-cache \
-    gcc \
-    g++ \
-    musl-dev \
-    sqlite-dev \
-    git
-
-WORKDIR /build
-
-# Copy go mod files
-COPY go.mod go.sum ./
-RUN go mod download
-
-# Copy source code
-COPY . .
-
-# Build with CGO enabled
-ARG TARGETOS
-ARG TARGETARCH
-ARG VERSION=dev
-ARG GIT_COMMIT=unknown
-ARG BUILD_TIME=unknown
-
-RUN CGO_ENABLED=1 GOOS=$TARGETOS GOARCH=$TARGETARCH \
-    go build -ldflags="-s -w \
-    -X main.Version=${VERSION} \
-    -X main.GitCommit=${GIT_COMMIT} \
-    -X main.BuildTime=${BUILD_TIME}" \
-    -o migrate ./cmd/migrate
-
-# Runtime stage
 FROM alpine:latest
 
 # Install runtime dependencies (including CGO/SQLite dependencies)
@@ -58,10 +18,14 @@ RUN apk add --no-cache \
 RUN addgroup -g 1000 gohoarder && \
     adduser -D -u 1000 -G gohoarder gohoarder
 
-# Copy binary from builder
-COPY --from=builder /build/migrate /usr/local/bin/migrate
+# Copy pre-built binary from GoReleaser
+# GoReleaser will automatically inject the correct binary for the target platform
+COPY migrate /usr/local/bin/migrate
 RUN chmod +x /usr/local/bin/migrate
 
+# Copy migration SQL files
+COPY migrations /migrations
+
 WORKDIR /app
 USER gohoarder