Bugfix: copyright_checker should reference //:docs_sources

## Description

The copyright_checker target currently references the `"docs"` directory directly, but should reference `//:docs_sources` filegroup instead for consistency with other S-CORE repos and to ensure all documentation files are scanned. Right now the copyright_checker doesn't actually check our documentation source files, but rather the bazel build directory files.

## Current Behavior

```python
copyright_checker(
name = "copyright",
srcs = [
".github",
"docs", # Direct directory reference
"examples",
"score",
"tools",
"//:BUILD",
"//:MODULE.bazel",
],
)
```

## Expected Behavior

Should reference the `docs_sources` filegroup created by the `docs()` macro:

```python
copyright_checker(
name = "copyright",
srcs = [
".github",
"//:docs_sources", # Use filegroup
"examples",
"score",
"tools",
"//:BUILD",
"//:MODULE.bazel",
],
)
```