fix(website): install git + scope docker context for Railway

The docs now consume github:@rivet-dev/docs-theme, so the build needs git for
pnpm to resolve it (apk add git). Add a Dockerfile-scoped .dockerignore that
narrows the repo-root build context to the website subtree, so the multi-GB
monorepo isn't uploaded — without touching the shared root .dockerignore or the
repo's other Dockerfiles. Verified: docker build -f frontend/packages/website/Dockerfile .

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Nathan Flurry

frontend/packages/website/Dockerfile

@@ -1,6 +1,7 @@
 FROM node:22-alpine AS build
 WORKDIR /app
-RUN npm install -g pnpm@9
+# git is required for pnpm to resolve the github: @rivet-dev/docs-theme dependency.
+RUN apk add --no-cache git && npm install -g pnpm@9
 
 # Copy website package
 COPY frontend/packages/website/package.json ./

frontend/packages/website/Dockerfile.dockerignore

@@ -0,0 +1,13 @@
+# Scoped to the website Dockerfile only (BuildKit uses <dockerfile>.dockerignore
+# when present). Narrows the repo-root build context to the website subtree so
+# the multi-GB monorepo isn't uploaded — without affecting the shared root
+# .dockerignore or the other Dockerfiles in this repo.
+*
+!frontend
+frontend/*
+!frontend/packages
+frontend/packages/*
+!frontend/packages/website
+**/node_modules
+**/dist
+**/.astro