update docs: remove preview warning, update sandboxes, mark preview integrations

- Remove private research preview warning from quick-start page
- Update sandboxes section on how-fabro-works to list all 6 providers
- Mark exe.dev and Sprites as (preview) in sidebar nav titles

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/core-concepts/how-fabro-works.mdx

@@ -67,15 +67,18 @@ When the engine hits a [parallel fan-out node](/workflows/stages-and-nodes#paral
 
 ## Sandboxes
 
-Node handlers execute tools (bash commands, file edits) inside a **sandbox**. Fabro supports three sandbox modes:
+Node handlers execute tools (bash commands, file edits) inside a **sandbox**. Fabro supports six sandbox providers:
 
 | Sandbox | Description |
 |---|---|
 | `local` | Tools run directly on the host machine (default) |
 | `docker` | Tools run inside a Docker container |
-| `daytona` | Tools run in a cloud sandbox with SSH access |
+| `daytona` | Tools run in a cloud VM with SSH access |
+| `ssh` | Tools run on any existing SSH host |
+| `exe` | Tools run in a fast ephemeral VM from [exe.dev](https://exe.dev) |
+| `sprites` | Tools run in a persistent VM from [Sprites](https://sprites.dev) |
 
-The sandbox is configured per-run via CLI flags (`--sandbox docker`) or the run config TOML.
+The sandbox is configured per-run via CLI flags (`--sandbox docker`) or the run config TOML. See [Environments](/execution/environments) for details on each provider.
 
 ## Events and observability
 

docs/getting-started/quick-start.mdx

@@ -3,10 +3,6 @@ title: "Quick Start"
 description: "Get up and running with Fabro"
 ---
 
-<Warning>
-  Fabro is in private research preview. Contact [bryan@qlty.sh](mailto:bryan@qlty.sh) if you're interested in trying it.
-</Warning>
-
 <Note>
 Fabro has two modes:
 

docs/integrations/exe-dev.mdx

@@ -1,5 +1,5 @@
 ---
-title: "exe.dev"
+title: "exe.dev (preview)"
 description: "Run Fabro workflows in fast ephemeral VMs from exe.dev"
 ---
 

docs/integrations/sprites.mdx

@@ -1,5 +1,5 @@
 ---
-title: "Sprites"
+title: "Sprites (preview)"
 description: "Run Fabro workflows in persistent Sprites VMs from Fly.io"
 ---