feat(ui): persistent literal-space toggle on the command line

'>' button after the Command: label turns the leading-'>' literal-space
behavior into a mode: while on, Space stays in the line instead of
submitting, until toggled off. State persists in settings.json; a
hand-typed leading '>' still works for a single line.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/settings.rs

@@ -112,6 +112,10 @@ pub struct UserSettings {
     /// Linked plugin source repositories (`owner/repo`) the marketplace installs
     /// from.
     pub plugin_repos: Vec<String>,
+    /// Command-line literal-space mode: when on, Space stays in the input
+    /// instead of submitting (as if every line started with `>`), until the
+    /// user toggles it back off.
+    pub literal_spaces: bool,
     /// Controls whether the TEXTEDIT command repeats automatically (0 = Multiple, 1 = Single).
     pub texteditmode: bool,
     /// TEXTFILL: fill TrueType glyphs (true) or draw them hollow (false).
@@ -143,6 +147,7 @@ impl Default for UserSettings {
             default_assoc_prompted: false,
             disabled_plugins: Vec::new(),
             plugin_repos: Vec::new(),
+            literal_spaces: false,
             texteditmode: false,
             textfill: true,
             backup_on_save: true,