refactor(api): Change filesAvailable signal to pass list by value

[DLST316]

Summary

This Pull Request modifies the IModRepositoryBridge::filesAvailable signal to pass the list of file info objects by value (QList<ModRepositoryFileInfo>) instead of by a list of raw pointers (QList<ModRepositoryFileInfo*>).

This is a prerequisite change required to fix a critical dangling pointer bug in the main ModOrganizer2 application.

Context: The Downstream Bug

In the main application's repository, a critical dangling pointer bug was identified in NexusBridge::nxmFilesAvailable. This bug could lead to random application crashes. The full context and discussion can be found in the original Pull Request here:

ModOrganizer2/modorganizer#2288

During the discussion in that PR, it was determined that the root cause was the unsafe, pointer-based design of the filesAvailable signal in this IModRepositoryBridge interface.

Design Rationale: Modification vs. Addition

As discussed in the original PR, a key decision was whether to modify the existing signal or add a new, overloaded one for backward compatibility.

This PR modifies the existing signal directly. This is a deliberate breaking change made for the following reasons:

1. Eliminating Unsafe Patterns: The original pointer-based signature is inherently dangerous and led to the bug. Leaving this "trap" in the API for future use would be a long-term risk to the stability of the codebase.
2. Maintainer Guidance: The project maintainer explicitly suggested that "a proper fix would be to modify the interface to not pass pointers." This change directly implements that guidance.
3. Improving API Safety: By enforcing a value-based signature, we guarantee that consumers of this API cannot accidentally misuse pointers, making the entire system more robust and safe.

BREAKING CHANGE

The signature of the IModRepositoryBridge::filesAvailable signal has been changed from const QList<ModRepositoryFileInfo*>& to const QList<ModRepositoryFileInfo>&.

All classes that implement this interface or slots that connect to this signal must be updated to handle a value-based QList.