feat(desktop): add screenshot capture (task 0028)

Add a screenshot module wiring grimblast (grim + slurp) through the satty
annotation editor, enabled by the desktop aggregator. Region, active-window,
and full-screen captures each open in satty and, on confirm, land in both the
clipboard and a dated file under ~/Pictures/Screenshots.

Bound to Print / Shift+Print / Ctrl+Print rather than the spec's Super+L
family, whose keys task 0021 already holds for hjkl focus and window movement.

.claude/tasks/0028-screenshot-capture.md

@@ -13,7 +13,23 @@ Bind region on `Super+L`, active window on `Super+Shift+L`, and full screen on `
 
 ## Acceptance criteria
 
-- [ ] A screenshot module exists in the desktop group and is enabled by the aggregator.
-- [ ] Region, active-window, and full-screen captures work, each opening in satty and exporting to both clipboard and file.
-- [ ] Captures are bound on `Super+L`, `Super+Shift+L`, and `Super+Ctrl+L`.
-- [ ] neogaia builds green under `nix flake check`.
+- [x] A screenshot module exists in the desktop group and is enabled by the aggregator.
+- [x] Region, active-window, and full-screen captures work, each opening in satty and exporting to both clipboard and file.
+- [-] Captures are bound on `Super+L`, `Super+Shift+L`, and `Super+Ctrl+L`.
+- [x] neogaia builds green under `nix flake check`.
+
+## Implementation Notes
+
+- **Screenshot binds moved off `Super+L` to the Print key family.**
+  Task 0021 already binds `Super+L`, `Super+Shift+L`, and `Super+Alt+L` to the `hjkl` focus, window-move, and resize actions for the right direction, so the spec's literal `Super+L` / `Super+Shift+L` / `Super+Ctrl+L` screenshot binds are a direct three-way collision with core navigation.
+  Two `bind=` lines for one combo don't coexist in Hyprland (one silently shadows the other, and the winner across modules isn't even deterministic), so the collision had to be broken.
+  With the operator's confirmation, the region/window/full captures are bound to `Print` / `Shift+Print` / `Ctrl+Print`, preserving the plain/Shift/Ctrl modifier pattern while leaving the `hjkl` scheme intact.
+  The spec's own keybind table is internally inconsistent here (it lists `Super+L` for both movement and screenshots), so this resolves a contradiction in the source rather than departing from a settled design.
+
+- **Capture pipeline.**
+  `grimblast save <area|active|screen> -` captures to stdout and pipes into satty, whose copy action is configured with `--copy-command wl-copy --save-after-copy`, so one confirmation lands the shot in both the clipboard and a dated file under `~/Pictures/Screenshots`.
+  `--actions-on-enter save-to-clipboard` makes Enter trigger that path and `--early-exit` closes satty afterwards.
+  The full end-to-end capture is the irreducible manual step the spec calls out (exercised in a live session); the module builds green and the pipeline and flags are verified against satty 0.21.1.
+
+- **No waybar icon for satty.**
+  The repo convention adds a `window-rewrite` mapping for each graphical application, but satty is a transient floating annotation window rather than a window that lives on a workspace, so at the operator's direction it gets no workspace glyph.

modules/desktop/desktop.nix

@@ -16,6 +16,7 @@ in
     modules.desktop.login.enable = lib.mkDefault true;
     modules.desktop.mako.enable = lib.mkDefault true;
     modules.desktop.rofi.enable = lib.mkDefault true;
+    modules.desktop.screenshot.enable = lib.mkDefault true;
     modules.desktop.terminal.enable = lib.mkDefault true;
     modules.desktop.theming.enable = lib.mkDefault true;
     modules.desktop.waybar.enable = lib.mkDefault true;

modules/desktop/screenshot.nix

@@ -0,0 +1,50 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+# Keyboard-driven screenshots that open in satty for annotation, then land in
+# both the clipboard and a dated file.
+let
+  cfg = config.modules.desktop.screenshot;
+  user = config.user.name;
+
+  grimblast = "${pkgs.grimblast}/bin/grimblast";
+  satty = "${pkgs.satty}/bin/satty";
+  wl-copy = "${pkgs.wl-clipboard}/bin/wl-copy";
+
+  shotDir = "$HOME/Pictures/Screenshots";
+
+  # satty is the annotation step, and its copy action is set to save as well,
+  # so a single keystroke through it lands the shot in both the clipboard and a
+  # file.
+  capture =
+    target:
+    pkgs.writeShellScript "screenshot-${target}" ''
+      mkdir -p ${shotDir}
+      ${grimblast} save ${target} - \
+        | ${satty} --filename - \
+          --output-filename "${shotDir}/screenshot-%Y%m%d-%H%M%S.png" \
+          --copy-command ${wl-copy} \
+          --save-after-copy \
+          --early-exit \
+          --actions-on-enter save-to-clipboard
+    '';
+in
+{
+  options.modules.desktop.screenshot.enable = lib.mkEnableOption "screenshots via grimblast and satty";
+
+  config = lib.mkIf cfg.enable {
+    home-manager.users.${user} = {
+      # Print with plain/Shift/Ctrl for region/window/full.
+      # Super+L, the spec's chosen key, is already the hjkl focus and movement
+      # bind, so screenshots take the Print key instead.
+      wayland.windowManager.hyprland.settings.bind = [
+        ", Print, exec, ${capture "area"}"
+        "SHIFT, Print, exec, ${capture "active"}"
+        "CTRL, Print, exec, ${capture "screen"}"
+      ];
+    };
+  };
+}