feat(home): add satty for screenshot annotation

Added satty (Wayland-native screenshot annotation tool) and integrated it with the Capture flow.
Wired `$mod SHIFT, Print` to slurp a region and open satty.
Added "Annotate region" to the rofi Capture menu (Tools > Capture).
Added satty's configuration via home-manager to inject the active theme's palette colors into its UI.

Verified: V1 (flake check --no-build, home activation package build).
Pending: V3 hardware/visual check for the satty UI (queued in HARDWARE-QUEUE.md).

agent/HARDWARE-QUEUE.md

@@ -312,6 +312,12 @@ QA machine), the **T14s** (webcam case).
       Same on a whole-swap bar (summer/boreal/executive-slate). If calcurse
       was removed from home.packages, the click toasts "calcurse isn't
       installed" instead of doing nothing.
+- [ ] **Screenshot annotation (satty)** (iteration #73) — after `home-update`:
+      hit SUPER+SHIFT+Print (or Tools ▸ Capture ▸ Annotate region) → a region
+      select (slurp) appears, then the `satty` UI opens in fullscreen with the
+      screenshot loaded. Check that the UI draws on the current theme palette
+      (tools colored properly) and hitting save places the screenshot in
+      `~/Pictures/Screenshots/` while hitting copy places it in the clipboard.
 
 ## AMD dev box only
 - [ ] **AMD runtime bits** — VA-API (`vainfo` → radeonsi), amd-pstate EPP