refactor: update viewport effects to use dynamic visible dimensions

Update viewport effects to use dynamic visible dimensions.

viewport_effects() now takes visible_rows and visible_cols parameters
instead of hardcoded 20/8 values.

Scrolling logic uses these parameters:
- row_offset updates when nr >= row_offset + visible_rows
- col_offset updates when nc >= col_offset + visible_cols

Default registry initialized with visible_rows=20, visible_cols=8
for MoveSelection, MovePanelCursor, and other commands.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/Qwen3.5-35B-A3B-GGUF:Q5_K_M)

src/command/cmd.rs

@@ -267,21 +267,25 @@ fn viewport_effects(
     nc: usize,
     old_row_offset: usize,
     old_col_offset: usize,
+    visible_rows: usize,
+    visible_cols: usize,
 ) -> Vec<Box<dyn Effect>> {
     let mut effects: Vec<Box<dyn Effect>> = vec![effect::set_selected(nr, nc)];
     let mut row_offset = old_row_offset;
     let mut col_offset = old_col_offset;
+    let vr = visible_rows.max(1);
+    let vc = visible_cols.max(1);
     if nr < row_offset {
         row_offset = nr;
     }
-    if nr >= row_offset + 20 {
-        row_offset = nr.saturating_sub(19);
+    if nr >= row_offset + vr {
+        row_offset = nr.saturating_sub(vr - 1);
     }
     if nc < col_offset {
         col_offset = nc;
     }
-    if nc >= col_offset + 8 {
-        col_offset = nc.saturating_sub(7);
+    if nc >= col_offset + vc {
+        col_offset = nc.saturating_sub(vc - 1);
     }
     if row_offset != old_row_offset {
         effects.push(Box::new(effect::SetRowOffset(row_offset)));
@@ -309,7 +313,7 @@ impl Cmd for MoveSelection {
         let col_max = self.cursor.col_count.saturating_sub(1);
         let nr = (self.cursor.row as i32 + self.dr).clamp(0, row_max as i32) as usize;
         let nc = (self.cursor.col as i32 + self.dc).clamp(0, col_max as i32) as usize;
-        viewport_effects(nr, nc, self.cursor.row_offset, self.cursor.col_offset)
+        viewport_effects(nr, nc, self.cursor.row_offset, self.cursor.col_offset, self.cursor.visible_rows, self.cursor.visible_cols)
     }
 }
 
@@ -764,7 +768,7 @@ impl Cmd for EnterAdvance {
         } else {
             (r, c) // already at bottom-right; stay
         };
-        viewport_effects(nr, nc, self.cursor.row_offset, self.cursor.col_offset)
+        viewport_effects(nr, nc, self.cursor.row_offset, self.cursor.col_offset, self.cursor.visible_rows, self.cursor.visible_cols)
     }
 }
 
@@ -2459,6 +2463,8 @@ pub fn default_registry() -> CmdRegistry {
                     col_count: 0,
                     row_offset: 0,
                     col_offset: 0,
+                    visible_rows: 20,
+                    visible_cols: 8,
                 },
             }))
         },
@@ -2539,6 +2545,8 @@ pub fn default_registry() -> CmdRegistry {
                     col_count: 0,
                     row_offset: 0,
                     col_offset: 0,
+                    visible_rows: 20,
+                    visible_cols: 8,
                 },
             }))
         },
@@ -2562,6 +2570,8 @@ pub fn default_registry() -> CmdRegistry {
                     col_count: 0,
                     row_offset: 0,
                     col_offset: 0,
+                    visible_rows: 20,
+                    visible_cols: 8,
                 },
             }))
         },
@@ -2796,7 +2806,7 @@ pub fn default_registry() -> CmdRegistry {
             let delta = args[1].parse::<i32>().map_err(|e| e.to_string())?;
             let (current, max) = match panel {
                 Panel::Formula => (ctx.formula_cursor, ctx.model.formulas().len()),
-                Panel::Category => (ctx.cat_panel_cursor, ctx.model.category_names().len()),
+                Panel::Category => (ctx.cat_panel_cursor, ctx.cat_tree_len()),
                 Panel::View => (ctx.view_panel_cursor, ctx.model.views.len()),
             };
             Ok(Box::new(MovePanelCursor {