feat: add NodePalette and PipelineCanvas components for enhanced flow node management

- Introduced NodePalette component to display draggable nodes categorized by type.
- Implemented PipelineCanvas component to manage the flow of nodes and connections.
- Integrated drag-and-drop functionality for adding nodes to the canvas.
- Created a catalog of node types with associated metadata for rendering in the palette.
- Established conversion functions between pipeline definitions and React Flow state.
- Added inspector for editing node properties and managing connections.
- Updated Next.js configuration for production and development environments.
- Removed obsolete embed.go file and added nginx configuration for serving the app.
- Updated package dependencies including @xyflow/react for enhanced functionality.
- Added TypeScript definitions for CSS imports to support styling in components.

Dockerfile

@@ -1,21 +1,13 @@
-# --- web build stage ---
-FROM node:22-alpine AS web
-WORKDIR /app
-COPY web/package.json web/package-lock.json* ./web/
-RUN cd web && (test -f package-lock.json && npm ci --no-fund --no-audit || npm install --no-fund --no-audit)
-COPY web ./web
-RUN cd web && npm run build
+# API server only — no UI, no web build stage.
+# The UI lives in its own container (web/Dockerfile) and proxies /api here.
 
-# --- go build stage ---
 FROM golang:1.24-alpine AS build
 WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
 COPY . .
-COPY --from=web /app/web/out ./web/out
 RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags='-s -w' -o /out/flow ./cmd/flow
 
-# --- runtime stage ---
 FROM alpine:3.20
 RUN apk add --no-cache ca-certificates tzdata
 COPY --from=build /out/flow /usr/local/bin/flow