tools/local-dev: docker-compose stack for UI development

Adds tools/local-dev/ with postgres + redis + mailpit + backend +
gateway plus a Make wrapper, so `make -C tools/local-dev up` brings
the full authenticated stack online and `pnpm -C ui/frontend dev`
talks to it directly. The committed `.env.development` already
points at the stack and pins the matching gateway response public
key from the dev keypair under tools/local-dev/keys/.

The backend ships a new opt-in env, BACKEND_AUTH_DEV_FIXED_CODE
(`tools/local-dev/.env` defaults it to 123456). When set,
ConfirmEmailCode accepts that literal in addition to the real
bcrypt-verified code; SendEmailCode still queues a real email so
Mailpit captures the issued code at http://localhost:8025/, and
both paths coexist. The override is rejected as non-six-digit by
config validation and emits a loud warning at backend startup.

The local-dev Dockerfiles mirror backend/Dockerfile and
gateway/Dockerfile but switch the runtime stage to alpine so
docker-compose healthchecks can wget /healthz; the gateway
Dockerfile additionally copies ui/core/ into the build context
because gateway/go.mod's `replace galaxy/core => ../ui/core` is
required to compile the gateway main.

Smoke tested:
- `make -C tools/local-dev up` boots all five services to healthy.
- send-email-code + confirm-email-code with code=123456 returns a
  device_session_id; a real code in Mailpit also redeems
  successfully.
- `pnpm test` 14/14, `pnpm exec playwright test` 44/44.
- `go test ./backend/internal/config/...` green.

Docs: tools/local-dev/README.md, tools/local-dev/keys/README.md,
new "Local development stack" section in ui/docs/testing.md, and a
short pointer in ui/README.md.

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

ui/README.md

@@ -132,6 +132,24 @@ make android         Capacitor + gradle                         Phase 32+
 make all             every target above
 ```
 
+## Local development
+
+For UI work against a real stack, the `tools/local-dev/` docker
+compose brings up postgres + redis + mailpit + backend + gateway in
+one command, and `ui/frontend/.env.development` is already wired to
+talk to it:
+
+```sh
+make -C tools/local-dev up        # build + start, wait for healthy
+pnpm -C ui/frontend dev           # Vite on the host
+# UI:     http://localhost:5173
+# Mailpit: http://localhost:8025
+```
+
+The stack accepts a fixed dev code (`123456`) in addition to the
+real Mailpit-delivered one. Full runbook in
+[`../tools/local-dev/README.md`](../tools/local-dev/README.md).
+
 ## Per-phase docs
 
 Topic docs live under `ui/docs/` and are added per phase as they're

ui/docs/testing.md

@@ -83,6 +83,32 @@ go test -count=1 \
   ./pkg/storage/... ./pkg/transcoder/... ./pkg/util/...
 ```
 
+## Local development stack
+
+For UI work that needs a real authenticated stack (verifying the
+FlatBuffers wire end-to-end, exercising a real lobby flow, hitting
+real Mailpit), bring up `tools/local-dev/`:
+
+```sh
+make -C tools/local-dev up        # postgres + redis + mailpit + backend + gateway
+pnpm -C ui/frontend dev           # Vite on the host, talks to the stack
+```
+
+`ui/frontend/.env.development` already targets the stack
+(`http://localhost:8080`) and pins the matching response-signing
+public key from `tools/local-dev/keys/`. Per-developer overrides go
+into `.env.development.local` (gitignored).
+
+The stack honours `BACKEND_AUTH_DEV_FIXED_CODE` (default `123456` in
+`tools/local-dev/.env`) so the login form takes that literal in
+addition to the real Mailpit code; see
+[`../../tools/local-dev/README.md`](../../tools/local-dev/README.md)
+for the full runbook (regenerating the dev keypair, switching the
+mode off, troubleshooting common boot issues).
+
+The local-dev stack is independent from the local-ci stack below;
+they bind different ports and can run side by side.
+
 ## Local CI verification
 
 `tools/local-ci/` ships a self-contained Gitea + Actions runner via

ui/frontend/.env.development

@@ -0,0 +1,12 @@
+# Vite picks this file up automatically when running in `development`
+# mode (`pnpm dev`, `pnpm test:e2e`). It targets the local-dev stack
+# brought up by `make -C tools/local-dev up`. Per-developer overrides
+# live in `.env.development.local` (gitignored by Vite convention).
+
+# Gateway public REST + Connect-Web edge listener.
+VITE_GATEWAY_BASE_URL=http://localhost:8080
+
+# Standard non-URL-safe base64 of the gateway response-signing public
+# key. Pairs with `tools/local-dev/keys/gateway-response.pem`. The pair
+# is dev-only — see `tools/local-dev/keys/README.md` before rotating.
+VITE_GATEWAY_RESPONSE_PUBLIC_KEY=nIG54tCuNiIKrazt8Hh7YxmmU/BhpseGhIIgj164Chw=

ui/frontend/.env.example

@@ -1,18 +1,17 @@
 # Vite reads any variable prefixed with `VITE_` and exposes it on
-# `import.meta.env`. Copy this file to `.env.local` (gitignored) and
-# fill in the values before running `pnpm run dev` or `pnpm exec
-# playwright test` against a real gateway.
+# `import.meta.env`. The committed `.env.development` already targets
+# the `tools/local-dev/` docker stack — most contributors don't need
+# to copy this file. Use a `.env.development.local` (gitignored by
+# Vite convention) for per-developer overrides, or use `.env.local`
+# when running `pnpm exec playwright test` against a non-default
+# gateway.
 
 # Base URL of the gateway public REST surface and Connect-Web edge
-# listener. Both surfaces share the same host and port. Defaults to
-# the local dev address used by `tools/local-ci` and the Go-side
-# integration suite.
+# listener. Both surfaces share the same host and port.
 VITE_GATEWAY_BASE_URL=http://localhost:8080
 
 # Standard (non-URL-safe) base64 of the gateway's raw 32-byte
-# Ed25519 response-signing public key. Required only for
-# authenticated unary calls; unauthenticated routes (`/login`)
-# work without it. For local dev, take the value the gateway
-# integration container exports as `ResponseSignerPublic` (see
-# `integration/testenv/gateway.go`).
+# Ed25519 response-signing public key. The local-dev stack ships a
+# checked-in keypair under `tools/local-dev/keys/`; for any other
+# environment, take the value from the gateway operator.
 VITE_GATEWAY_RESPONSE_PUBLIC_KEY=