fix(detection): Fix FileNotFoundError on user_credentials.csv, deprecated rerun methods, and SMTP fallback in Signature Verification Portal #1734

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Describe the bug

The Streamlit web application for Signature Verification in projects/detection/Signature_Verification_Portal/app.py cannot start and encounters runtime exceptions:

1. FileNotFoundError on startup:
   Line 12 attempts to read user_credentials.csv directly from the current working directory without checking if it exists:

   user_data = pd.read_csv("user_credentials.csv")

   Because user_credentials.csv is not present in the repository, any attempt to run streamlit run app.py crashes immediately with:
   FileNotFoundError: [Errno 2] No such file or directory: 'user_credentials.csv'
   Additionally, using raw relative paths fails if the user starts Streamlit from the repository root.

2. Deprecated st.experimental_rerun() Calls:
   app.py and Dashboard.py repeatedly call st.experimental_rerun(), which is deprecated and removed in recent Streamlit releases in favor of st.rerun().

3. Hardcoded SMTP Credentials and Unhandled Network Errors:
   Lines 35-36 hardcode personal credentials for Gmail SMTP. If SMTP connection fails or environment variables are not configured, attempting to reset a password crashes the entire application instead of handling errors gracefully.

4. Redundant Non-Standard Dependency in requirements.txt:
   requirements.txt contains db-sqlite3, an outdated third-party package; Python includes native sqlite3 in the standard library.

Expected behavior

1. app.py should safely resolve user_credentials.csv relative to the script directory and automatically initialize an empty credentials DataFrame with the required schema (username, password) if the file does not exist yet.
2. The application should use st.rerun() when available and fallback to st.experimental_rerun() for backward compatibility.
3. Password reset and SMTP calls should handle exceptions gracefully and allow environment variable overrides (SMTP_SENDER_EMAIL, SMTP_SENDER_PASSWORD).
4. requirements.txt should clean up dependencies and remove redundant db-sqlite3.

Proposed Changes

1. Initialize user_credentials.csv safely in app.py with relative path handling (os.path.join(os.path.dirname(__file__), ...)).
2. Replace hardcoded relative CSV paths across insert_user, update_password, and update_password_in_database.
3. Add resilient rerun helper function supporting both st.rerun and st.experimental_rerun.
4. Wrap SMTP sending in try-except blocks with configurable environment variable fallbacks.
5. Clean up requirements.txt.

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