Put text fill and the command-line preferences on the Display page

Three settings that work, persist, and could only be reached by typing their
name: TEXTFILL, CLIPROMPTLINES and COMMANDLINEFADETIME. The last two govern
how much of the command window is prompt and how long its history lingers —
the kind of thing people fiddle with once and then leave, which is exactly
what a settings dialog is for.

One fix rides along. TEXTFILL is a process-global, so changing it invalidates
the text in every open drawing; the SETVAR path rebuilt only the active tab,
leaving the others rendering the previous setting until an unrelated edit
happened to rebuild them. Both paths now go through
`invalidate_text_everywhere`, so the checkbox and the command cannot disagree.

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

src/app/mod.rs

@@ -2011,6 +2011,12 @@ pub enum Message {
     SaveTimeChanged(i32),
     /// Toggle keeping a `.bak` copy when overwriting a drawing (ISAVEBAK).
     BackupOnSaveChanged(bool),
+    /// Toggle filled TrueType glyphs (TEXTFILL).
+    TextFillChanged(bool),
+    /// Change how many prompt lines sit above the command window (CLIPROMPTLINES).
+    ClipromptLinesChanged(i32),
+    /// Change how long command-line history lines stay visible (COMMANDLINEFADETIME).
+    CommandLineFadeChanged(i32),
     /// Restore Model Space display/canvas appearance to defaults.
     RestoreModelSpaceDisplayDefaults,
     /// Restore Selection visual effect settings to defaults.