feat(build): embed static assets into Go binary

Embed frontend build output directly into Go binary using //go:embed.
This removes runtime dependency on ../frontend/public/ path and
simplifies Docker builds by serving assets from embedded filesystem.

- Add backend/web/embed.go with embed.FS directive
- Update server to serve from embedded static assets
- Update Makefile to copy frontend build to web/static/
- Update Dockerfile for simplified multi-stage build
- Update frontend package.json output paths
- Remove custom 'oc' command from flake.nix dev shell

Dockerfile

@@ -1,70 +1,30 @@
-# Multi-stage build for Aethera
-# Stage 1: Build frontend assets
+# Step 1: Build Frontend
 FROM oven/bun:1 AS frontend-builder
-
 WORKDIR /app/frontend
-
-# Copy frontend package files
 COPY frontend/package.json frontend/bun.lock ./
-
-# Install dependencies
 RUN bun install --frozen-lockfile
-
-# Copy frontend source code
 COPY frontend/ ./
-
-# Build frontend assets
 RUN bun run build
 
-# Stage 2: Build Go binary
+# Stage 2: Build Backend
 FROM golang:1.25-alpine AS backend-builder
-
 WORKDIR /app
-
-# Install build dependencies
 RUN apk add --no-cache git
-
-# Copy go mod files
 COPY backend/go.mod backend/go.sum ./
-
-# Download Go dependencies
 RUN go mod download
-
-# Copy backend source code
 COPY backend/ ./
+COPY --from=frontend-builder /app/frontend/public/ ./web/static/
+RUN go build -ldflags="-w -s" -o aethera ./cmd
 
-# Copy frontend assets from previous stage
-COPY --from=frontend-builder /app/frontend/public/dist ./public/dist
-COPY --from=frontend-builder /app/frontend/public/index.html ./public/
-COPY --from=frontend-builder /app/frontend/public/pages ./public/pages
-
-# Build the Go binary
-RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o aethera ./cmd
-
-# Stage 3: Create minimal runtime image
+# Stage 3: Minimal Runtime
 FROM alpine:3.21
-
-# Install ca-certificates for HTTPS calls
 RUN apk add --no-cache ca-certificates
-
 WORKDIR /app
-
-# Copy the binary from the builder stage
 COPY --from=backend-builder /app/aethera .
-
-# Copy static assets
-COPY --from=backend-builder /app/public ./public
-
-# Create data directory
 RUN mkdir -p /app/data
 
-# Expose the default port
 EXPOSE 8080
-
-# Set environment variable defaults
 ENV AETHERA_LISTEN=0.0.0.0
 ENV AETHERA_PORT=8080
 ENV AETHERA_DATA_DIR=/app/data
-
-# Set the entrypoint
 ENTRYPOINT ["./aethera"]