feat: initialize project skeleton with Go backend, database, and config

- Go module with standard library + gorilla/sessions + mysql driver
- Config: env-based configuration with .env file support
- Database: MySQL connection with auto-migration for 6 tables
- Seed data: 12 system tags with options, 8 system snippets
- Auth: session cookie middleware
- Handlers: auth, tags, snippets, builder, claude, dashboard, suggestions, settings
- LLM: OpenAI-compatible client with 30s timeout
- Docker: Dockerfile + docker-compose.yml
- .env.example with all configuration options

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

Dockerfile

@@ -0,0 +1,18 @@
+FROM golang:1.22-alpine AS builder
+
+WORKDIR /app
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -o server .
+
+FROM alpine:latest
+RUN apk --no-cache add ca-certificates
+
+WORKDIR /app
+COPY --from=builder /app/server .
+COPY --from=builder /app/frontend ./frontend
+
+EXPOSE 8080
+CMD ["./server"]