feat: date parsing, component extraction, and wizard formulas

Extend FieldProposal with chrono-based date format detection and
configurable component extraction (Year, Month, Quarter). Add
ConfigureDates and DefineFormulas wizard steps to ImportPipeline.
build_model injects derived date categories and parses formula strings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/command/dispatch.rs

@@ -241,6 +241,7 @@ fn import_headless(
             })
             .collect(),
         model_name: model_name.unwrap_or("Imported Model").to_string(),
+        formulas: vec![],
     };
 
     match pipeline.build_model() {