Feature: Create a "Search My Library" Page to Unify Keyword and Semantic Search

[amanvatss]

The current app has two separate search pages: Query Stored Summaries (keyword) and Semantic Search (FAISS) (vector). This is confusing.

This issue is to combine them into a single new page, 📚 Search My Library, with one search bar and a toggle to select the search mode.

Acceptance Criteria:

• Remove Query Stored Summaries and Semantic Search from the sidebar st.radio.
• Add a new 📚 Search My Library option to the sidebar.
• This new page must have:
  • A single st.text_input for the query.
  • A st.radio to select mode: Keyword or Semantic.
  • A single "Search" button.
• Clicking "Search" calls query_db if Keyword is selected.
• Clicking "Search" calls search_similar if Semantic is selected.
• Results from both functions are displayed in st.expander elements.

Files to Modify:

• streamlit_app.py