refactor(core): centralize formatting logic

Move formatting logic to a new `format` module and update `main.rs` and
`persistence` to use it.

- Create `src/format.rs` with shared formatting functions.
- Update `src/main.rs` to include the `format` module.
- Refactor `src/persistence/mod.rs` to use the new `display_text` logic via
  `GridLayout` .

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/gemma-4-26B-A4B-it-GGUF:UD-Q5_K_XL)

src/format.rs

@@ -0,0 +1,50 @@
+use crate::model::cell::CellValue;
+
+/// Format a CellValue for display with number formatting options.
+pub fn format_value(v: Option<&CellValue>, comma: bool, decimals: u8) -> String {
+    match v {
+        Some(CellValue::Number(n)) => format_f64(*n, comma, decimals),
+        Some(CellValue::Text(s)) => s.clone(),
+        None => String::new(),
+    }
+}
+
+/// Parse a number format string like ",.0" into (use_commas, decimal_places).
+pub fn parse_number_format(fmt: &str) -> (bool, u8) {
+    let comma = fmt.contains(',');
+    let decimals = fmt
+        .rfind('.')
+        .and_then(|i| fmt[i + 1..].parse::<u8>().ok())
+        .unwrap_or(0);
+    (comma, decimals)
+}
+
+/// Format an f64 with optional comma grouping and decimal places.
+pub fn format_f64(n: f64, comma: bool, decimals: u8) -> String {
+    let formatted = format!("{:.prec$}", n, prec = decimals as usize);
+    if !comma {
+        return formatted;
+    }
+    let (int_part, dec_part) = if let Some(dot) = formatted.find('.') {
+        (&formatted[..dot], Some(&formatted[dot..]))
+    } else {
+        (&formatted[..], None)
+    };
+    let is_neg = int_part.starts_with('-');
+    let digits = if is_neg { &int_part[1..] } else { int_part };
+    let mut result = String::new();
+    for (idx, c) in digits.chars().rev().enumerate() {
+        if idx > 0 && idx % 3 == 0 {
+            result.push(',');
+        }
+        result.push(c);
+    }
+    if is_neg {
+        result.push('-');
+    }
+    let mut out: String = result.chars().rev().collect();
+    if let Some(dec) = dec_part {
+        out.push_str(dec);
+    }
+    out
+}

src/main.rs

@@ -1,5 +1,6 @@
 mod command;
 mod draw;
+mod format;
 mod formula;
 mod import;
 mod model;

src/persistence/mod.rs

@@ -458,17 +458,7 @@ pub fn export_csv(model: &Model, view_name: &str, path: &Path) -> Result<()> {
             out.push(',');
         }
         let row_values: Vec<String> = (0..layout.col_count())
-            .map(|ci| {
-                if layout.is_records_mode() {
-                    layout.records_display(ri, ci).unwrap_or_default()
-                } else {
-                    layout
-                        .cell_key(ri, ci)
-                        .and_then(|key| model.evaluate_aggregated(&key, &layout.none_cats))
-                        .map(|v| v.to_string())
-                        .unwrap_or_default()
-                }
-            })
+            .map(|ci| layout.display_text(model, ri, ci, false, 0))
             .collect();
         out.push_str(&row_values.join(","));
         out.push('\n');