feat(themes): add executive-slate professional dark theme

Leveraged Nano Banana to generate a 4k functional minimalist wallpaper. Added the new preset with a solid, high-legibility waybar and flat rofi launcher.

themes/executive-slate/rofi.rasi

@@ -0,0 +1,79 @@
+/* 
+ * Executive Slate Rofi Theme
+ * Clean, flat, functional, professional.
+ */
+
+* {
+    background-color: transparent;
+    text-color: var(text, #D4DAE8);
+    font: "Inter 13";
+}
+
+window {
+    width: 600px;
+    background-color: var(base, #1A1D24);
+    border: 1px solid var(overlay, #333947);
+    border-radius: 4px;
+    padding: 16px;
+}
+
+mainbox {
+    spacing: 12px;
+}
+
+inputbar {
+    background-color: var(surface, #232731);
+    border: 1px solid var(overlay, #333947);
+    border-radius: 4px;
+    padding: 10px 14px;
+    spacing: 10px;
+    children: [ prompt, entry ];
+}
+
+prompt {
+    text-color: var(accent, #4D78CC);
+}
+
+entry {
+    placeholder: "Type to filter...";
+    placeholder-color: var(subtext, #8792A6);
+}
+
+listview {
+    lines: 7;
+    spacing: 4px;
+    scrollbar: false;
+    border: 0px;
+}
+
+element {
+    padding: 8px 14px;
+    border-radius: 4px;
+    spacing: 12px;
+}
+
+element normal.normal, element alternate.normal {
+    background-color: transparent;
+}
+
+/* Functional highlight: solid surface color with a subtle accent edge */
+element selected.normal {
+    background-color: var(surface, #232731);
+    text-color: var(text, #D4DAE8);
+    border: 0 0 0 4px solid;
+    border-color: var(accent, #4D78CC);
+}
+
+element-icon {
+    size: 24px;
+    background-color: transparent;
+}
+
+element-text {
+    background-color: transparent;
+    vertical-align: 0.5;
+}
+
+element-text selected {
+    text-color: var(text, #D4DAE8);
+}