0.6.3: image previews, Hyprland-scale fix, password reveal, Keybinds editor

Wallpaper: file picker moved off the deprecated FileChooserDialog to
gtk4::FileDialog, plus a "Browse ~/Pictures/Backgrounds" thumbnail
grid (recursive scan, decoded previews) so picking a wallpaper isn't
guessing blind from filenames.

Fixed the app becoming unusable at Hyprland scale > 1.0: the sidebar's
~30-row nav list had no ScrolledWindow, so its unscrollable minimum
height exceeded the logical screen size once scale shrank it below
~1000px, clipping the window (Save buttons included) with no way to
reach the rest. Sidebar now scrolls independently; content column's
minimum width also dropped 760->560 for the same reason at scale 2.0.

Wi-Fi/saved-network password fields had no way to unhide what you
typed. Swapped every masked Entry (network.rs, breadcrumbs.rs, and the
shared password_row widget) to gtk4::PasswordEntry, which has a native
reveal-icon toggle.

Added a Keybinds editor for hypr/binds.json -- the one JSON Hyprland
config (globals/common/per-layout binds) with no GUI anywhere in the
app, despite Display/Appearance/Startup Apps all having one for their
own JSON config. Action-specific fields (command/direction/workspace/
options/...) round-trip through a compact inline-JSON column rather
than hardcoding a widget per action shape.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bos-settings"
-version = "0.6.2"
+version = "0.6.3"
 edition = "2021"
 
 [dependencies]