refactor(persistence): improve Markdown formula and category handling

Update persistence logic for formulas and categories.

- Formulas targeting `_Measure` no longer include the category suffix in
  Markdown.
- `_Measure` items are now excluded from the category section in Markdown
  to avoid duplication with the formulas section.
- Improved Markdown parsing to correctly handle formulas without an
  explicit category suffix, defaulting them to `_Measure` .
- Added logic to skip virtual index and dimension categories during
  persistence.

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

src/persistence/mod.rs

@@ -205,16 +205,38 @@ pub fn format_md(model: &Model) -> String {
     if !model.formulas().is_empty() {
         w!(out, "\n## Formulas");
         for f in model.formulas() {
-            w!(out, "- {} [{}]", f.raw, f.target_category);
+            if f.target_category == "_Measure" {
+                w!(out, "- {}", f.raw);
+            } else {
+                w!(out, "- {} [{}]", f.raw, f.target_category);
+            }
         }
     }
 
     // ── Categories (items comma-separated on one line) ───────────────
+    // Collect formula targets so we can exclude them from _Measure items
+    let formula_targets: std::collections::HashSet<&str> = model
+        .formulas()
+        .iter()
+        .filter(|f| f.target_category == "_Measure")
+        .map(|f| f.target.as_str())
+        .collect();
+
     for cat in model.categories.values() {
+        use crate::model::category::CategoryKind;
+        // Skip _Index and _Dim — they are fully virtual, never persisted
+        if matches!(cat.kind, CategoryKind::VirtualIndex | CategoryKind::VirtualDim) {
+            continue;
+        }
         w!(out, "\n## Category: {}", cat.name);
         let mut bare: Vec<String> = Vec::new();
         let mut grouped: Vec<String> = Vec::new();
         for item in cat.items.values() {
+            // For _Measure, skip items that are formula targets
+            // (they'll be recreated from the ## Formulas section)
+            if cat.kind == CategoryKind::VirtualMeasure && formula_targets.contains(item.name.as_str()) {
+                continue;
+            }
             match &item.group {
                 Some(g) => grouped.push(format!("{}[{}]", quote_name(&item.name), quote_name(g))),
                 None => bare.push(quote_name(&item.name)),
@@ -372,8 +394,13 @@ pub fn parse_md(text: &str) -> Result<Model> {
                                     raw[..i].to_string(),
                                     raw[i + 2..raw.len() - 1].to_string(),
                                 ));
+                                continue;
                             }
                         }
+                        // No [Category] suffix — default to _Measure
+                        if !raw.is_empty() && raw.contains('=') {
+                            formulas.push((raw, "_Measure".to_string()));
+                        }
                     }
                 }
             }