feat: add dev/prod deployment templates and workflow

[shaikhhasib]

Description

Added environment-specific config templates:
.env.dev.example
.env.prod.example

Added environment-specific Docker Compose definitions:
docker-compose.dev.yml for local/dev stack (db, redis, api, monitor, worker
docker-compose.prod.yml for runtime services (api, monitor, worker) using external DB/Redis from env file

Added CI/CD workflow draft:
deploy-dev-prod.yml
Builds and pushes a single immutable image to GHCR
Deploys to dev on main pushes
Deploys to prod on v* tags

Added deployment runbook:
DEPLOYMENT.md with deploy, migration, and rollback steps

Added inline workflow comments to explain deployment decisions and expected secrets.

Motivation

This change is required to separate development and production deployment paths while keeping one codebase.
It solves these problems:

   Dev and prod configuration were mixed/hardcoded in compose.
   No dedicated workflow existed for controlled promotion from dev to prod.
   Deployment steps and operational expectations were undocumented.

Design decisions:
Single image artifact for api/monitor/worker
Environment-specific runtime via .env.dev/.env.prod
Dev auto-deploy from main; prod deploy from release tags.

[YektaY]

Closing this PR, parts of this work was integrated into #39