Add init flags to Offset and set vertical offset

Add `value_initiated` and `max_initiated` flags to prevent
repeated assignments. Provide `set_initial_value` for one‑time
initialisation and use it to centre the vertical offset when
creating the board widget. Remove stale comments on cell size constants.

src/app/states/skirmish.rs

@@ -5,23 +5,40 @@ use clap::ValueEnum;
 pub struct Offset {
     value: usize,
     max: usize,
+    value_initiated: bool,
+    max_initiated: bool,
 }
 
 impl Offset {
     pub fn new() -> Self {
-        Self { value: 0, max: 0 }
+        Self {
+            value: 0,
+            max: 0,
+            value_initiated: false,
+            max_initiated: false,
+        }
     }
 
     pub fn get_value(&self) -> usize {
         self.value
     }
 
+    pub fn set_initial_value(&mut self, value: usize) {
+        if self.value_initiated {
+            return;
+        }
+
+        self.value = value;
+        self.value_initiated = true;
+    }
+
     pub fn set_max(&mut self, max: usize) {
-        if self.max != 0 {
+        if self.max_initiated {
             return;
         }
 
         self.max = max;
+        self.max_initiated = true;
     }
 
     pub fn next(&mut self) {