Improve fresh local setup flow

[nsteve-one]

Closes #597

Summary

This makes the documented fresh-clone path work from the repo root:

git clone https://github.com/Merit-Systems/echo.git
cd echo
pnpm i
pnpm dev

What I found

On current master, a fresh local run failed after Docker and the router server started because echo-control ran Prisma without a local DATABASE_URL:

Error: Environment variable not found: DATABASE_URL.
  --> prisma/schema.prisma:9

The README also sent new contributors straight to pnpm i without listing the required tools, and one workspace example printed an npm dedupe / workspace:* error during pnpm i.

Changes

• Runs the existing echo-control local setup automatically before root pnpm dev.
• Hardens packages/app/control/scripts/setup.sh so it creates .env from .env.example, fills an empty AUTH_SECRET, and ensures the local Docker PostgreSQL DATABASE_URL is present without overwriting populated values.
• Updates the root README with the verified fresh-clone workflow and prerequisites.
• Skips the npm dedupe postinstall command when the next-402-chat workspace example is being installed by pnpm, removing the scary but ignored workspace:* install error.

Verification

• npx -y pnpm@10.11.0 install
• npx -y pnpm@10.11.0 dev
• curl -I http://localhost:3000 returned HTTP/1.1 200 OK
• curl http://localhost:3069/health returned {"status":"healthy", ...}
• npx -y pnpm@10.11.0 -C packages/sdk/examples/next-402-chat run postinstall
• npx -y pnpm@10.11.0 exec prettier --check README.md package.json packages/sdk/examples/next-402-chat/package.json
• bash -n packages/app/control/scripts/setup.sh
• git diff --check

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