fix numbering, text editor, and selection handling

Separate file/folder numbering by default, with shared numbering
option in the numbering rule popup. Text editor now loads names
from previous pipeline steps instead of originals, and uses
absolute position so it works correctly with any numbering mode.
Folders sort before files for consistent ordering. Spacebar
works in the text editor textarea without triggering drag.

crates/nomina-core/src/lib.rs

@@ -49,6 +49,7 @@ pub type Result<T> = std::result::Result<T, NominaError>;
 pub struct RenameContext {
     pub index: usize,
     pub total: usize,
+    pub absolute_index: usize,
     pub original_name: String,
     pub extension: String,
     pub path: PathBuf,
@@ -65,6 +66,7 @@ impl RenameContext {
         Self {
             index,
             total: 1,
+            absolute_index: index,
             original_name: String::new(),
             extension: String::new(),
             path: PathBuf::new(),