Implement working screenshot capture with wlr-screencopy

- Fixed brace mismatch and duplicate code in screenshot.rs
- Increased SHM pool size to 256MB for high-res displays
- Corrected wlr-screencopy protocol usage: send copy request in Buffer event
- Fixed background handling: set_background now updates LockedSurface.background
- Removed dummy background creation; screenshots set when ready
- Added format conversion for Xbgr8888 and Xrgb8888 to ARGB32
- Proper Y-inversion handling based on flags

The lock screen now displays captured screenshots as background.
Screenshots are taken immediately after lock, before UI is shown.
Matches swaylock-effects behavior: lock appears first, then screenshot
applies when ready (no blocking).

Fixes: black/red screen issues, screenshot not displaying.

Cargo.lock

@@ -645,6 +645,21 @@ dependencies = [
  "miniz_oxide",
 ]
 
+[[package]]
+name = "futures"
+version = "0.3.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b147ee9d1f6d097cef9ce628cd2ee62288d963e16fb287bd9286455b241382d"
+dependencies = [
+ "futures-channel",
+ "futures-core",
+ "futures-executor",
+ "futures-io",
+ "futures-sink",
+ "futures-task",
+ "futures-util",
+]
+
 [[package]]
 name = "futures-channel"
 version = "0.3.32"
@@ -652,6 +667,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "07bbe89c50d7a535e539b8c17bc0b49bdb77747034daa8087407d655f3f7cc1d"
 dependencies = [
  "futures-core",
+ "futures-sink",
 ]
 
 [[package]]
@@ -671,6 +687,12 @@ dependencies = [
  "futures-util",
 ]
 
+[[package]]
+name = "futures-io"
+version = "0.3.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cecba35d7ad927e23624b22ad55235f2239cfa44fd10428eecbeba6d6a717718"
+
 [[package]]
 name = "futures-macro"
 version = "0.3.32"
@@ -682,6 +704,12 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "futures-sink"
+version = "0.3.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c39754e157331b013978ec91992bde1ac089843443c49cbc7f46150b0fad0893"
+
 [[package]]
 name = "futures-task"
 version = "0.3.32"
@@ -694,9 +722,13 @@ version = "0.3.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "389ca41296e6190b48053de0321d02a77f32f8a5d2461dd38762c0593805c6d6"
 dependencies = [
+ "futures-channel",
  "futures-core",
+ "futures-io",
  "futures-macro",
+ "futures-sink",
  "futures-task",
+ "memchr",
  "pin-project-lite",
  "slab",
 ]
@@ -2057,11 +2089,13 @@ dependencies = [
 name = "wayrustlock"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "cairo-rs",
  "chrono",
  "clap",
  "env_logger",
  "fastblur",
+ "futures",
  "image",
  "log",
  "pam-client",
@@ -2072,6 +2106,7 @@ dependencies = [
  "users",
  "wayland-client",
  "wayland-protocols",
+ "wayland-protocols-wlr",
  "xkbcommon",
  "zeroize",
 ]