Migrate to bread-utils: Hyprland IPC, single-instance lock, popup scaffold

Replaces three hand-rolled pieces of code with the new shared bread-utils
crate (path dependency for now, see the TODO in breadbox/Cargo.toml):

- get_active_workspace's raw socket1 client -> bread_utils::hypr
- toggle_or_continue's TOCTOU-prone PID-file dance -> bread_utils::singleton
  (flock-based, no read-then-write race)
- the layer-shell window setup, Up/Down visible-row navigation, and
  click-outside-close gesture -> bread_utils::gtk_popup

Builds and tests clean across the whole breadbox workspace.

Cargo.lock

@@ -37,11 +37,23 @@ dependencies = [
  "serde_json",
 ]
 
+[[package]]
+name = "bread-utils"
+version = "0.2.3"
+dependencies = [
+ "dirs",
+ "gtk4",
+ "gtk4-layer-shell",
+ "serde",
+ "serde_json",
+]
+
 [[package]]
 name = "breadbox"
 version = "0.2.7"
 dependencies = [
  "bread-theme",
+ "bread-utils",
  "breadbox-shared",
  "gtk4",
  "gtk4-layer-shell",