feat(import): add Label field support for high-cardinality per-row data

Add support for Label-kind categories to handle high-cardinality
per-row fields like descriptions, IDs, and notes. These fields are
stored alongside regular categories but default to Axis::None and
are excluded from pivot category limits.

Changes:
- analyzer.rs: Label fields now default to accepted=true
- wizard.rs: Collect and process label fields during model building,
  attaching label values as coordinates for each cell
- category.rs: Add Label variant to CategoryKind enum
- types.rs: Add add_label_category() method and update category
  counting to only include Regular-kind categories

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/Qwen3.5-35B-A3B-GGUF:Q5_K_M)

src/import/wizard.rs

@@ -94,6 +94,11 @@ impl ImportPipeline {
             .iter()
             .filter(|p| p.accepted && p.kind == FieldKind::Measure)
             .collect();
+        let labels: Vec<&FieldProposal> = self
+            .proposals
+            .iter()
+            .filter(|p| p.accepted && p.kind == FieldKind::Label)
+            .collect();
 
         if categories.is_empty() {
             return Err(anyhow!("At least one category must be accepted"));
@@ -139,6 +144,11 @@ impl ImportPipeline {
             model.add_category(derived_name)?;
         }
 
+        // Create label categories (stored but not pivoted by default)
+        for lab in &labels {
+            model.add_label_category(&lab.field)?;
+        }
+
         if !measures.is_empty() {
             model.add_category("Measure")?;
             if let Some(cat) = model.category_mut("Measure") {
@@ -187,6 +197,28 @@ impl ImportPipeline {
                     continue;
                 }
 
+                // Attach label values as coords (missing labels become "").
+                for lab in &labels {
+                    let val = map
+                        .get(&lab.field)
+                        .and_then(|v| v.as_str())
+                        .map(|s| s.to_string())
+                        .or_else(|| {
+                            map.get(&lab.field).and_then(|v| {
+                                if v.is_null() {
+                                    None
+                                } else {
+                                    Some(v.to_string())
+                                }
+                            })
+                        })
+                        .unwrap_or_default();
+                    if let Some(cat) = model.category_mut(&lab.field) {
+                        cat.add_item(&val);
+                    }
+                    coords.push((lab.field.clone(), val));
+                }
+
                 for measure in &measures {
                     if let Some(val) = map.get(&measure.field).and_then(|v| v.as_f64()) {
                         let mut cell_coords = coords.clone();