Add Namma Metro ridership dashboard and README

- Introduced a new Streamlit application in `main.py` to display Namma Metro ridership data from a JSONL file.
- Added a README file with installation instructions for running the Streamlit app.

Author: traffic-kowshik

apps/namma_metro/README.md

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+# README
+
+```bash
+pip install streamlit
+streamlit run apps/namma_metro/main.py
+```

apps/namma_metro/main.py

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+import streamlit as st
+import json
+import pandas as pd
+from pathlib import Path
+
+from traffic_data_bengaluru.utils import *
+
+data_directory = get_data_directory()
+ridership_filepath = data_directory / "namma_metro" / "raw" / "ridership.jsonl"
+
+st.title("🚇 Namma Metro")
+st.set_page_config(page_title="Namma Metro Ridership", layout="wide")
+
+records = []
+with open(ridership_filepath, "r") as f:
+    for line in f:
+        item = json.loads(line)
+        results = item.get("results", [])
+        if results:
+            records.append(results[0])
+
+if not records:
+    st.warning("No ridership data found.")
+else:
+    df = pd.DataFrame(records).sort_values(by='RidershipDate', ascending=False)
+    st.dataframe(df)