Add rustfmt configuration and reformat code

- Document new Rust formatting standards in AGENTS, CODE_MAP, and
  PROGRESS.
- Add rustfmt.toml with style 2024, 2‑space indents, 100‑char width, LF
  endings.
- Apply consistent 2‑space indentation and ordering across source files.
- Minor clean‑up of imports and whitespace to match the new style.

src/app/states/skirmish_states/marked_cells.rs

@@ -3,17 +3,17 @@ use std::collections::VecDeque;
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct MarkedCells {
-    pub marking_cells: bool,
-    pub marked_cells: VecDeque<(usize, usize)>,
-    pub selected_unit: Option<Units>,
+  pub marking_cells: bool,
+  pub marked_cells: VecDeque<(usize, usize)>,
+  pub selected_unit: Option<Units>,
 }
 
 impl MarkedCells {
-    pub fn new() -> Self {
-        Self {
-            marking_cells: false,
-            marked_cells: VecDeque::new(),
-            selected_unit: None,
-        }
+  pub fn new() -> Self {
+    Self {
+      marking_cells: false,
+      marked_cells: VecDeque::new(),
+      selected_unit: None,
     }
+  }
 }