feat: add Coastfile for local development

Add a Coastfile so developers can use Coasts to run isolated dev
environments with the full stack (Next.js, backend worker, zoekt,
Postgres, Redis) in parallel for worktree-based workflows.

AUTH_URL is set via the Coastfile command using the WEB_DYNAMIC_PORT
env var that Coast injects at runtime. No changes to .env.development
needed.

Fixes #1056

Author: dahyman91

.env.development

@@ -12,7 +12,7 @@ CTAGS_COMMAND=ctags
 # openssl rand -base64 33
 # @see: https://authjs.dev/getting-started/deployment#auth_secret
 AUTH_SECRET="00000000000000000000000000000000000000000000"
-AUTH_URL="http://localhost:${WEB_DYNAMIC_PORT:-3000}"
+AUTH_URL="http://localhost:3000"
 # AUTH_CREDENTIALS_LOGIN_ENABLED=true
 
 DATA_CACHE_DIR=${PWD}/.sourcebot  # Path to the sourcebot cache dir (ex. ~/sourcebot/.sourcebot)

Coastfile

@@ -23,7 +23,7 @@ cache = ["bin"]
 # Next.js frontend + API
 [services.web]
 install = ["cd /workspace && (test -f node_modules/.yarn-state.yml || DATABASE_URL=postgresql://postgres:postgres@host.docker.internal:5432/postgres make yarn)", "cd /workspace && test -f config.json || echo {} > config.json", "cd /workspace && DATABASE_URL=postgresql://postgres:postgres@host.docker.internal:5432/postgres yarn dev:prisma:migrate:dev"]
-command = "cd /workspace && DATABASE_URL=postgresql://postgres:postgres@host.docker.internal:5432/postgres REDIS_URL=redis://host.docker.internal:6379 yarn dev:web"
+command = "cd /workspace && AUTH_URL=http://localhost:${WEB_DYNAMIC_PORT:-3000} DATABASE_URL=postgresql://postgres:postgres@host.docker.internal:5432/postgres REDIS_URL=redis://host.docker.internal:6379 yarn dev:web"
 port = 3000
 restart = "on-failure"
 cache = ["node_modules"]