feat(docker): publish ready-to-use iklobato/lightapi image

[iklobato]

Summary

Adds an official Docker image so users can run a fully-functional LightAPI
server by mounting a YAML config — no Python install, no build step.

docker run --rm -p 8000:8000 \
    -v "$(pwd)/lightapi.yaml:/app/lightapi.yaml:ro" \
    -e DATABASE_URL=sqlite:////app/data.db \
    iklobato/lightapi:latest

What ships

• Dockerfile — python:3.12-slim, installs lightapi[async] + psycopg2-binary, drops to a non-root user. LIGHTAPI_VERSION build arg pins the wheel.
• docker/entrypoint.py — loads /app/lightapi.yaml (overridable via LIGHTAPI_CONFIG), builds the Starlette app, and starts uvicorn with proxy_headers=True.
• docker/lightapi.example.yaml — minimal config used as a smoke-test fixture.
• .github/workflows/docker-publish.yml — multi-arch (linux/amd64, linux/arm64) build that pushes to iklobato/lightapi on master push and on v*.*.* tags.
• docs/deployment/docker.md — complete rewrite covering quickstart, env vars, docker compose + PostgreSQL, JWT-auth setup, and the publish pipeline.
• README.md — added a Docker quickstart block.

Verified locally

docker build --build-arg LIGHTAPI_VERSION=0.1.21 -t lightapi:smoke .
docker run -d --rm --name lightapi-smoke -p 18000:8000 \
    -v "$(pwd)/docker/lightapi.example.yaml:/app/lightapi.yaml:ro" \
    -e DATABASE_URL=sqlite:////tmp/data.db lightapi:smoke

All endpoints returned correct responses: empty list → POST creates row → GET returns it with pagination envelope.

Required setup before merge

The workflow needs two repository secrets. Before merging this PR:

gh secret set DOCKERHUB_USERNAME --body "iklobato"
gh secret set DOCKERHUB_TOKEN    --body "<your-dockerhub-access-token>"

The Docker Hub token needs Read, Write, Delete scope on iklobato/lightapi (generate at https://hub.docker.com/settings/security).

Tag schedule

Event	Tags pushed
Push of v0.1.22	iklobato/lightapi:0.1.22, :0.1, :latest
Push to master	iklobato/lightapi:master
Manual workflow_dispatch	iklobato/lightapi:manual-<run-number>

Test plan

• Local docker build succeeds on darwin/arm64
• docker run with the example YAML responds 200/201 on documented routes
• Set DOCKERHUB_USERNAME + DOCKERHUB_TOKEN secrets
• docker-publish.yml succeeds on master merge
• docker pull iklobato/lightapi:latest works from an unrelated machine