Add CSV import functionality

- Use csv crate for robust CSV parsing (handles quoted fields, empty values, \r\n)
- Extend --import command to auto-detect format by file extension (.csv or .json)
- Reuse existing ImportPipeline and analyzer for field type detection
- Categories detected automatically (string fields), measures for numeric fields
- Updated help text and welcome screen to mention CSV support

All 201 tests pass.

src/main.rs

@@ -54,26 +54,40 @@ impl Runnable for CmdLineArgs {
         // Load or create model
         let model = get_initial_model(&self.file_path)?;
 
-        // Pre-TUI import: parse JSON and open wizard
-        let import_json = if let Some(ref path) = self.import_path {
+        // Pre-TUI import: parse JSON or CSV and open wizard
+        let import_value = if let Some(ref path) = self.import_path {
             match std::fs::read_to_string(path) {
                 Err(e) => {
                     eprintln!("Cannot read '{}': {e}", path.display());
                     return Ok(());
                 }
-                Ok(content) => match serde_json::from_str::<serde_json::Value>(&content) {
-                    Err(e) => {
-                        eprintln!("JSON parse error: {e}");
-                        return Ok(());
+                Ok(content) => {
+                    if path.to_string_lossy().ends_with(".csv") {
+                        // Parse CSV and wrap as JSON array
+                        match crate::import::csv_parser::parse_csv(&path.to_string_lossy()) {
+                            Ok(records) => Some(serde_json::Value::Array(records)),
+                            Err(e) => {
+                                eprintln!("CSV parse error: {e}");
+                                return Ok(());
+                            }
+                        }
+                    } else {
+                        // Parse JSON
+                        match serde_json::from_str::<serde_json::Value>(&content) {
+                            Err(e) => {
+                                eprintln!("JSON parse error: {e}");
+                                return Ok(());
+                            }
+                            Ok(json) => Some(json),
+                        }
                     }
-                    Ok(json) => Some(json),
-                },
+                }
             }
         } else {
             None
         };
 
-        run_tui(model, self.file_path, import_json)
+        run_tui(model, self.file_path, import_value)
     }
 }
 
@@ -130,7 +144,7 @@ impl Runnable for HelpArgs {
         println!("improvise — multi-dimensional data modeling TUI\n");
         println!("USAGE:");
         println!("  improvise [file.improv]         Open or create a model");
-        println!("  improvise --import data.json    Import JSON then open TUI");
+        println!("  improvise --import data.json    Import JSON (or CSV) then open TUI");
         println!("  improvise --cmd '{{...}}'         Run a JSON command (headless, repeatable)");
         println!("  improvise --script cmds.jsonl   Run commands from file (headless)");
         println!("\nTUI KEYS (vim-style):");
@@ -246,13 +260,13 @@ impl<'a> Drop for TuiContext<'a> {
 fn run_tui(
     model: Model,
     file_path: Option<PathBuf>,
-    import_json: Option<serde_json::Value>,
+    import_value: Option<serde_json::Value>,
 ) -> Result<()> {
     let mut stdout = io::stdout();
     let mut tui_context = TuiContext::enter(&mut stdout)?;
     let mut app = App::new(model, file_path);
 
-    if let Some(json) = import_json {
+    if let Some(json) = import_value {
         app.start_import_wizard(json);
     }
 
@@ -518,7 +532,7 @@ fn draw_welcome(f: &mut Frame, area: Rect) {
         ),
         ("", Style::default()),
         (
-            ":import <file.json>    Import a JSON file",
+            ":import <file>         Import JSON or CSV file",
             Style::default().fg(Color::Cyan),
         ),
         (