feat: add window visibility percentage to frames and search API

[onehassan]

description

This PR introduces a new visible_percentage field to the frames table, enabling us to track and query how much of a window is visible on the screen. It includes updates across the migrations, Rust data structures, APIs, to support this feature. Visibility calculations consider the positions and overlap of multiple windows.

This enhancement is particularly useful when using the --capture-unfocused-windows flag. It allows users to precisely filter and distinguish search results based on the actual visibility of unfocused windows, greatly enhancing precision and relevance in scenarios with overlapping windows.

how to test

1. Build screenpipe and run it with the --capture-unfocused-windows flag
   ./target/release/screenpipe --disable-audio --enable-frame-cache --capture-unfocused-windows
2. Capture frames while windows overlap and verify that the visible_percentage field reflects the correct visibility percentage.
3. Perform searches with visibility filters using the new parameters min_visible_percentage and max_visible_percentage and verify correct filtering

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[github-actions]

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[louis030195]

this is cool and probably better than previous focus detection solution

does it work on windows and linux?

would like some testers