docs: document two-process dev workflow with Vite proxy

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -25,3 +25,20 @@ Forgejo Actions handles:
 - Container image build + push to the Forgejo registry on merge to `main` (`:main`) and on `v*` tags (`:<version>`).
 
 Task and milestone tracking: Fable (`Minstrel` project, id 12).
+
+## Development
+
+Minstrel has two concurrent dev processes:
+
+1. **Backend:** `docker compose up` — starts Postgres and Minstrel on `:4533`.
+2. **Frontend:** `cd web && npm install && npm run dev` — Vite dev server on `:5173` with HMR.
+
+The Vite dev server proxies `/api/*` and `/rest/*` to the backend on `:4533`,
+so session cookies work correctly when the SPA is loaded from the Vite origin.
+
+### Production build
+
+`docker build -t minstrel .` runs the SvelteKit build inside a `node` stage,
+copies the output into the `golang` stage, and `//go:embed`s it into the
+final binary. The resulting container serves the SPA from `/` alongside the
+API surfaces. No separate static-file server is required.