Add a source

A source is one file in sources/ of the configuration folder. Adding one changes no program.

Write ~/.config/sandcastle/sources/<name>.yaml:
```
name: recipes
destination:
  address: https://recipes.example.com/api/worker
  secret: recipes
poll_interval: 30s
capabilities: [claude]
max_jobs_per_hour: 30
job_timeout: 6m
```
Every key is required; each is in config.yaml. List in capabilities only what this source needs.

If the source lives inside your network, add internal: as in Reach a service inside your network.
Set the token the source gave you:
```
sandcastle secret set recipes
```
Restart the three pieces. The gate makes its list of names from the configuration when it starts, the keep its destinations, and the core its sources:
```
systemctl --user restart sandcastle.target
```
A job running at that moment is stopped.
Check:
```
sandcastle check
```
You want ok source recipes: reachable, <n> waiting. Any other line is in Check messages.

Remove a source