[Feature] Query Sourcecraft for existing packages

# Potential Solution
- https://api.staging.snapcraft.io/docs/bins.html#bin_find
- https://api.staging.snapcraft.io/docs/bins.html#bin_info

Example `bin_find`: `https://api.staging.snapcraft.io/v2/bins/find?q=yaml`
```
{
"results": [
{
"name": "go-github-go-yaml-yaml-v3",
"package-id": "7zMriCxPLPEK02xfQSLvSTWHZhORfZXg"
},
{
"name": "0xnishit-go-gopkg-yaml-v3",
"package-id": "2nJEdAfseayaapeGGKi5iANSgogA5UNz"
...
]
}
```

Example `bin_info`: `https://api.staging.snapcraft.io/v2/bins/info/0xnishit-go-gopkg-yaml-v3?fields=channel-map`
```
{
"channel-map": [
{
"channel": {
"name": "latest/edge",
"platform": {
"architecture": "amd64",
"channel": "24.04",
"name": "ubuntu"
},
"released-at": "2025-04-29T10:40:05.658127+00:00",
"risk": "edge",
"track": "latest"
}
}
],
"default-track": null,
"name": "0xnishit-go-gopkg-yaml-v3",
"package-id": "2nJEdAfseayaapeGGKi5iANSgogA5UNz"
}

```
## Algorithm
1. Search for the package using `bin_find` (or go straight to step 2)
2. Use `bin_info`
- 400 Error >> Resource Not Found
- 200 >> We get the channel information >> get the name (check that it matches)

If matches, we have the package name & name of the channel + platform
If not, we know we have to onboard this

**This step should be done during init**

## What Protocol We Need
- Standard Naming Convention >> `elts-`
- We want to make sure name of package & repo is the same

Start at the initialization flow in the Rust repository and trace how package and repository names are currently handled. Read the linked bin_find and bin_info API documentation, then verify the 400/200 paths, channel and platform data, and the elts- naming rule. Done means init can distinguish an existing matching package from one that must be onboarded.

Written by the indexing model from the issue text.