fix(rofi): resolve whole-swap launcher @import and page the app grid

The Apps launcher (`rofi -show drun -theme launcher`) imported
`custom.rasi` — the name HM gives *generated* themes — but a whole-swap
theme's base is deployed under its source basename (`rofi.rasi`), so the
import resolved against $HOME and rofi errored with "custom.rasi not
found" on every whole-swap theme. Make the default import track the
active base (rofi.rasi for whole-swaps, custom.rasi otherwise) and point
Boreal's own launcher.rasi at rofi.rasi.

Also give Boreal's app grid `flow: horizontal` so Down at a column's foot
pages to the next screen instead of jumping to the next column's top,
mirroring the theme-picker grid.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

themes/boreal/launcher.rasi

@@ -2,12 +2,13 @@
  * Boreal — app-launcher override (themes/<slug>/launcher.rasi).
  * Installed to ~/.local/share/rofi/themes/launcher.rasi and used only by
  * `rofi -show drun` (the SUPER+Space / SUPER+D launcher). It inherits the
- * frosted aurora panel from the sibling custom.rasi (the active theme),
+ * frosted aurora panel from the sibling rofi.rasi (this whole-swap theme,
+ * which HM deploys under its source basename — rofi.rasi — not custom.rasi),
  * then reshapes the list into a 4×3 grid of large application icons.
  * Text menus keep the list — they don't use this theme.
  */
 
-@import "custom.rasi"
+@import "rofi.rasi"
 
 window { width: 780px; }
 
@@ -17,6 +18,10 @@ listview {
     fixed-columns: true;
     spacing: 10px;
     padding: 6px 0px 0px 0px;
+    /* Fill row-by-row so Down at a column's foot pages to the next screen
+       instead of jumping to the top of the next column (rofi's default
+       Vertical flow). Mirrors the theme-picker grid in rofi.nix. */
+    flow: horizontal;
 }
 
 element {