feat: add Docker dev environment with live reload

[WilsonNet]

Summary

Adds a `docker-compose.dev.yml` for local development with automatic live reload for both backend and frontend. No existing files are modified.

• `docker-compose.dev.yml` — standalone dev stack using `manage.py runserver` (backend) and `pnpm dev` (frontend); same env file conventions as production
• `dashboard/Dockerfile.dev` — lightweight Node image running Vite dev server with `src/` and `public/` mounted for HMR
• `proxy/etc/nginx/templates/dev.conf.template` — dev nginx config that proxies `/` to Vite with WebSocket upgrade headers for HMR instead of serving static files
• `docs/dev-environment.md` — contributor docs covering setup, live reload mechanics, migration workflow, edge cases, loading DB dumps, and the Docker Desktop inode caveat with workarounds

How to use

cp .env.example .env
cd dashboard && cp .env.example .env && cd ..
# Edit .env: set DB_PASSWORD and DJANGO_SECRET_KEY
docker compose -f docker-compose.dev.yml up -d --build

Access at `http://localhost:9000\` (same URL as production).

Live reload mechanisms

• Backend — Django `manage.py runserver` with `StatReloader`; restarts automatically on any `.py` change. Chosen over gunicorn `--reload` which is unreliable with Docker volume mounts.
• Frontend — Vite HMR over WebSocket forwarded through nginx. CSS-only changes inject without touching JS; TSX errors show browser overlay and auto-recover on fix.

TanStack Router codegen fix (`TSR_TMP_DIR`)

TanStack Router generates `routeTree.gen.ts` by writing a temp file then atomically renaming it to the destination. Atomic rename means: write the full content to a throwaway file first, then swap it into place in one instant — so nobody ever sees a half-written file.

The problem in Docker: the rename was crossing two different filesystem address spaces:

• Temp file → `/dashboard/.tanstack/tmp/` (container's own internal storage)
• Destination → `/dashboard/src/routeTree.gen.ts` (host bind mount)

Linux forbids rename across different address spaces (EXDEV error), so the route tree was never updated when new route files were added.

Fix: `TSR_TMP_DIR=/dashboard/src/.tanstack-tmp` moves the temp file inside the `src/` bind mount. Now both paths live in the same address space and the rename succeeds. The `src/.tanstack-tmp/` directory is gitignored.

This works on all setups (native Docker Engine on Linux, Docker Desktop on Linux/macOS, OrbStack) because the fix is about keeping both ends of the rename inside the same bind mount entry — not about which OS or VM layer is underneath.

Test plan

• Stack builds and starts from scratch (`docker compose -f docker-compose.dev.yml up -d --build`)
• `http://localhost:9000\`, `http://localhost:5173\`, `http://localhost:8000/api/schema/\` all return 200
• Backend: add route + view → auto-reload → route serves correctly
• Backend: `makemigrations` + `migrate` forward → column appears in DB
• Backend: `migrate` backward → column removed from DB
• Backend: `settings.py` change → auto-reload, server stays up
• Backend: syntax error → container exits with clear traceback; recovers after fix + restart
• Frontend: edit component → `hmr update` in logs, browser updates
• Frontend: TSX syntax error → browser overlay, auto-recovers on fix
• Frontend: add new route file → `routeTree.gen.ts` auto-updated by Vite plugin (no manual steps)
• DB dump loading: `down -v` + `up -d` + `psql < dump.sql` sequence validated end-to-end

[giubrocchi]

Nice, thanks for the help!