Add Docker dev environment

[chetanr25]

Add docker/dev/ environment (source mount + reload)

Context

There is one root Dockerfile and one docker-compose.yml serving every purpose. We are splitting docker config per environment so dev and prod stop fighting each other. This issue covers the dev environment.

Goal

docker/
  dev/
    Dockerfile     # installs dev deps, mounts source, runs with --reload
    compose.yml    # app + ollama (+ any dev-only services)

Tasks

• docker/dev/Dockerfile: based on the backend package, installs .[dev] deps. Optimized for iteration, not size.
• docker/dev/compose.yml:
  • bind-mount the source so edits hot-reload
  • run uvicorn with --reload against the new backend.main app factory
  • ollama service
  • expose API on 8000 (configurable from .env)
• Confirm reload works on a code edit without rebuild.
• Update the path in Makefile later

Part of #512