feat: Implement database feature for system messages

Adds a database functionality to the PhotoReasoningScreen's system message section.

Key features:
- A "Database" button on the system message card opens a pop-up.
- The first pop-up lists saved system message entries with alternating dark yellow backgrounds.
  - A "New" button allows creating new entries.
  - Each entry has a 3-dot menu with a "Delete" option.
- The second pop-up allows creating or editing entries:
  - Fields for "Title" (placeholder "App/Task") and "Guide" (placeholder "Write a guide...").
  - Text fields have a white background; the pop-up has a dark yellow background.
  - A "Save" button saves the entry.
- Entries are stored in SharedPreferences using JSON serialization.
- Basic validation for empty fields and duplicate titles is included.
- Styling (rounded buttons, pop-up sizes, colors) implemented as per requirements.

Author: google-labs-jules[bot]