ui: pyramid colour stands out from the selection pinks (fix develop CI)

The pyramid5 colour added in #517 sat within the selection test's distance of
the hover pink (dark and light). Darker violet in both themes; the headless
palette matches.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/view.rs

@@ -62,7 +62,7 @@ impl Palette {
         hex: Rgb(0x78, 0x9c, 0xc0),
         tet: Rgb(0x80, 0xb4, 0x8a),
         wedge: Rgb(0xc0, 0xaa, 0x78),
-        pyramid: Rgb(0xa8, 0x90, 0xc8),
+        pyramid: Rgb(0x8c, 0x80, 0xb0),
         shell: Rgb(0xc0, 0x8c, 0x78),
         line_element: Rgb(0xc8, 0x8c, 0x1e),
         mesh_edge: Rgb(0x1e, 0x23, 0x2a),