fix: prevent learning mode from collapsing read paths to $HOME

Files directly under ~ (e.g., ~/.gitignore, ~/.npmrc) were collapsed
to the home directory, defeating sandboxing. Now keeps exact file paths
when the parent directory would be $HOME.

internal/sandbox/learning.go

@@ -220,9 +220,15 @@ func CollapsePaths(paths []string) []string {
 		}
 	}
 
-	// For standalone paths, use their parent directory
+	// For standalone paths, use their parent directory — but never collapse to $HOME
 	for _, p := range standalone {
-		result = append(result, filepath.Dir(p))
+		parent := filepath.Dir(p)
+		if parent == home {
+			// Keep exact file path to avoid opening entire home directory
+			result = append(result, p)
+		} else {
+			result = append(result, parent)
+		}
 	}
 
 	// Sort and deduplicate (remove sub-paths of other paths)