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/import/csv_parser.rs

@@ -0,0 +1,159 @@
+use anyhow::{Context, Result};
+use csv::ReaderBuilder;
+use serde_json::Value;
+
+/// Parse a CSV file and return records as serde_json::Value array
+pub fn parse_csv(path: &str) -> Result<Vec<Value>> {
+    let mut reader = ReaderBuilder::new()
+        .has_headers(true)
+        .flexible(true)
+        .trim(csv::Trim::All)
+        .from_path(path)
+        .with_context(|| format!("Failed to open CSV file: {path}"))?;
+
+    // Detect if first row looks like headers (strings) or data (mixed)
+    let has_headers = reader.headers().is_ok();
+
+    let mut records = Vec::new();
+    let mut headers = Vec::new();
+
+    if has_headers {
+        headers = reader
+            .headers()
+            .with_context(|| "Failed to read CSV headers")?
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+    }
+
+    for result in reader.records() {
+        let record = result.with_context(|| "Failed to read CSV record")?;
+        let mut map = serde_json::Map::new();
+
+        for (i, field) in record.iter().enumerate() {
+            let json_value: Value = parse_csv_field(field);
+            if has_headers {
+                if let Some(header) = headers.get(i) {
+                    map.insert(header.clone(), json_value);
+                }
+            } else {
+                map.insert(i.to_string(), json_value);
+            }
+        }
+
+        if !map.is_empty() {
+            records.push(Value::Object(map));
+        }
+    }
+
+    Ok(records)
+}
+
+fn parse_csv_field(field: &str) -> Value {
+    if field.is_empty() {
+        return Value::Null;
+    }
+
+    // Try to parse as number (integer or float)
+    if let Ok(num) = field.parse::<i64>() {
+        return Value::Number(serde_json::Number::from(num));
+    }
+
+    if let Ok(num) = field.parse::<f64>() {
+        return Value::Number(
+            serde_json::Number::from_f64(num).unwrap_or(serde_json::Number::from(0)),
+        );
+    }
+
+    // Otherwise treat as string
+    Value::String(field.to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs;
+    use tempfile::tempdir;
+
+    fn create_temp_csv(content: &str) -> (String, tempfile::TempDir) {
+        let dir = tempdir().unwrap();
+        let path = dir.path().join("test.csv");
+        fs::write(&path, content).unwrap();
+        (path.to_string_lossy().to_string(), dir)
+    }
+
+    #[test]
+    fn parse_simple_csv() {
+        let (path, _dir) = create_temp_csv("Region,Product,Revenue\nEast,Shirts,1000\nWest,Shirts,800");
+        let records = parse_csv(&path).unwrap();
+
+        assert_eq!(records.len(), 2);
+        assert_eq!(records[0]["Region"], Value::String("East".to_string()));
+        assert_eq!(records[0]["Product"], Value::String("Shirts".to_string()));
+        assert_eq!(records[0]["Revenue"], Value::Number(serde_json::Number::from(1000)));
+    }
+
+    #[test]
+    fn parse_csv_with_floats() {
+        let (path, _dir) =
+            create_temp_csv("Region,Revenue,Cost\nEast,1000.50,600.25\nWest,800.75,500.00");
+        let records = parse_csv(&path).unwrap();
+
+        assert_eq!(records.len(), 2);
+        assert!(records[0]["Revenue"].is_f64());
+        assert_eq!(records[0]["Revenue"], Value::Number(serde_json::Number::from_f64(1000.50).unwrap()));
+    }
+
+    #[test]
+    fn parse_csv_with_quoted_fields() {
+        let (path, _dir) = create_temp_csv("Product,Description,Price\n\"Shirts\",\"A nice shirt\",10.00");
+        let records = parse_csv(&path).unwrap();
+
+        assert_eq!(records.len(), 1);
+        assert_eq!(records[0]["Product"], Value::String("Shirts".to_string()));
+        assert_eq!(records[0]["Description"], Value::String("A nice shirt".to_string()));
+    }
+
+    #[test]
+    fn parse_csv_with_empty_values() {
+        let (path, _dir) = create_temp_csv("Region,Product,Revenue\nEast,,1000\nWest,Shirts,");
+        let records = parse_csv(&path).unwrap();
+
+        assert_eq!(records.len(), 2);
+        assert_eq!(records[0]["Product"], Value::Null);
+        assert_eq!(records[1]["Revenue"], Value::Null);
+    }
+
+    #[test]
+    fn parse_csv_mixed_types() {
+        let (path, _dir) = create_temp_csv(
+            "Name,Count,Price,Active\nWidget,5,9.99,true\nGadget,3,19.99,false",
+        );
+        let records = parse_csv(&path).unwrap();
+
+        assert_eq!(records.len(), 2);
+        assert_eq!(records[0]["Name"], Value::String("Widget".to_string()));
+        assert_eq!(records[0]["Count"], Value::Number(serde_json::Number::from(5)));
+        assert!(records[0]["Price"].is_f64());
+        assert_eq!(records[0]["Active"], Value::String("true".to_string()));
+    }
+
+    #[test]
+    fn parse_checking_csv_format() {
+        // Simulates the format of /Users/edwlan/Downloads/Checking1.csv
+        let (path, _dir) = create_temp_csv(
+            "Date,Amount,Flag,CheckNo,Description\n\
+             \"03/31/2026\",\"-50.00\",\"*\",\"\",\"VENMO PAYMENT 260331\"\n\
+             \"03/31/2026\",\"-240.00\",\"*\",\"\",\"ROBINHOOD DEBITS XXXXX3795\"",
+        );
+        let records = parse_csv(&path).unwrap();
+
+        assert_eq!(records.len(), 2);
+        assert_eq!(records[0]["Date"], Value::String("03/31/2026".to_string()));
+        assert_eq!(records[0]["Amount"], Value::Number(serde_json::Number::from_f64(-50.00).unwrap()));
+        assert_eq!(records[0]["Flag"], Value::String("*".to_string()));
+        assert_eq!(records[0]["CheckNo"], Value::Null);
+        assert_eq!(records[0]["Description"], Value::String("VENMO PAYMENT 260331".to_string()));
+        assert_eq!(records[1]["Amount"], Value::Number(serde_json::Number::from_f64(-240.00).unwrap()));
+    }
+}