Rename Foundry handoffs to tasks (#239)

* Restore foundry onboarding stack

* Consolidate foundry rename

* Create foundry tasks without prompts

* Rename Foundry handoffs to tasks

foundry/CONTRIBUTING.md

@@ -0,0 +1,64 @@
+# Contributing
+
+## Development Setup
+
+1. Clone:
+
+```bash
+git clone https://github.com/rivet-dev/sandbox-agent.git
+cd sandbox-agent/foundry
+```
+
+2. Install dependencies:
+
+```bash
+pnpm install
+```
+
+3. Build all packages:
+
+```bash
+pnpm -w build
+```
+
+## Package Layout
+
+- `packages/shared`: contracts/schemas
+- `packages/backend`: RivetKit actors + DB + providers + integrations
+- `packages/cli`: `hf` and `hf tui` (OpenTUI)
+
+## Local RivetKit Dependency
+
+Build local RivetKit before backend changes that depend on Rivet internals:
+
+```bash
+cd ../rivet
+pnpm build -F rivetkit
+
+cd /path/to/sandbox-agent/foundry
+just sync-rivetkit
+```
+
+## Validation
+
+Run before opening a PR:
+
+```bash
+pnpm -w typecheck
+pnpm -w build
+pnpm -w test
+```
+
+## Dev Backend (Docker Compose)
+
+Start the dev backend (hot reload via `bun --watch`) and Vite frontend via Docker Compose:
+
+```bash
+just foundry-dev
+```
+
+Stop it:
+
+```bash
+just foundry-dev-down
+```