feat: add Docker support for self-hosted deployment

[nothingtosurprise]

Summary

⚠️ IMPORTANT: NOT RUNTIME TESTED — PLEASE TEST BEFORE MERGING

This PR was developed and syntax-validated but NOT runtime-tested
due to environment limitations (developed on Android without Docker).

Before merging, please run:

• docker compose build — verify no build errors
• docker compose up -d — verify all 3 services start
• Frontend loads at http://localhost:3000
• API responds at http://localhost:3001/api/version
• Redis connects successfully

Community testing before merge is welcome!

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Summary

Adds complete Docker support enabling self-hosted deployment
without Vercel. Closes the self-hosted deployment roadmap item.

Type of change

• New feature
• CI / Build / Infrastructure

Files Added

• Dockerfile — multi-stage build (node:20-alpine + nginx:alpine)
• nginx.conf — SPA routing, gzip, API proxy
• docker-compose.yml — 3 services (app, api, redis)
• .env.example — Docker self-hosting variables added
• docker/server/Dockerfile — Express API container
• docker/server/package.json — express, cors, ioredis
• docker/server/index.js — 30+ routes replacing Vercel Edge Functions

Usage

cp .env.example .env
docker compose build
docker compose up -d

Frontend: http://localhost:3000

API: http://localhost:3001/api/version

Checklist

• No existing files modified
• Vercel deployment unaffected
• No API keys or secrets committed
• Runtime tested (needs desktop environment)

[vercel]

@nothingtosurprise is attempting to deploy a commit to the Elie Team on Vercel.

A member of the Team first needs to authorize it.

[nothingtosurprise]

Hi @koala73! Thanks for the review.

I understand the concerns. I'm happy to revise this to:

1. Remove docker/server/ entirely and use the existing /server
   TypeScript code instead
2. Update docker-compose.yml to build from the existing server
3. Any other changes you'd suggest

Would love your guidance on the preferred approach! 🙏