Suggest links

Pre-filled command runners at https://exe.dev/suggest

`https://exe.dev/suggest?command=<urlencoded-command>` opens a page in the
exe.dev dashboard that describes an action for review and possible approval.

These links are designed for agents (and humans) to hand off actions that an
agent cannot (and should not!) perform on the user's behalf.

## What can be suggested

Each link suggests one exe.dev command (what follows `ssh exe.dev`). For example:

- `share set-public mybox`
- `resize mybox --memory=4G`
- `new --name=snazzy-new-vm`

Not all commands and arguments are supported; see "preflight" below.

## Checking a link before sending it

Append `&preflight=1` and fetch the link:

```
curl -s 'https://exe.dev/suggest?command=share+set-public+mybox&preflight=1'
```

A 200 response means the command can be suggested, not that it will succeed.