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/helpers/main_menu_option.rs

@@ -1,13 +1,13 @@
 pub fn main_menu_option_helper(s: String) -> String {
-    if let Some(pos) = s
-        .char_indices()
-        .filter(|(_, c)| c.is_ascii_uppercase())
-        .nth(1)
-        .map(|(i, _)| i)
-    {
-        let (first, second) = s.split_at(pos);
-        format!("{first} {second}")
-    } else {
-        s
-    }
+  if let Some(pos) = s
+    .char_indices()
+    .filter(|(_, c)| c.is_ascii_uppercase())
+    .nth(1)
+    .map(|(i, _)| i)
+  {
+    let (first, second) = s.split_at(pos);
+    format!("{first} {second}")
+  } else {
+    s
+  }
 }