Refactor FindFileRecursively to skip excluded directories (bin/obj/.git/node_modules)

[Copilot]

FindFileRecursively used Directory.GetFiles(..., SearchOption.AllDirectories) — eager, unbounded, and unaware of the project's standard skip list — making it expensive on large workspaces.

Changes

• WorkspaceRootService.FindFileRecursively: replaced the single GetFiles call with an iterative stack-based DFS that applies DirectoryFilters.ShouldSkipDirectory before descending into any subdirectory
• Switched to Directory.EnumerateFiles / EnumerateDirectories (lazy) over the eager GetFiles / GetDirectories
• Separated exception handling for file and directory enumeration so an access failure on one doesn't suppress the other

// Before
var files = Directory.GetFiles(rootPath, fileName, SearchOption.AllDirectories);
return files.Length > 0 ? files[0] : null;

// After — skips bin/obj/.git/node_modules, lazy, per-directory error isolation
var stack = new Stack<string>();
stack.Push(rootPath);
while (stack.Count > 0)
{
    var currentDir = stack.Pop();
    foreach (var file in Directory.EnumerateFiles(currentDir, fileName))
        return file;
    foreach (var subDir in Directory.EnumerateDirectories(currentDir))
        if (!DirectoryFilters.ShouldSkipDirectory(subDir))
            stack.Push(subDir);
}
return null;

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