fix: Scale floating button icons proportionally on mobile viewports

Remove hardcoded width/height HTML attributes from iconify-icon elements
that were overriding CSS sizing. The iconify-icon component uses HTML
attributes for SVG rendering, ignoring CSS width/height.

- Remove width="28" height="28" from 8 button templates
- Remove conflicting 768px media query from _buttons.css
- Add default desktop icon sizes (24px) in _scroll-behavior.css
- Icons now scale via clamp() from 18px (380px) to 24px (900px)

templates/partials/widgets/cmd-k-button.html

@@ -0,0 +1,11 @@
+{{define "cmd-k-button"}}
+<!-- CMD+K Command Bar Button (Fixed Left - Last) -->
+<button
+    id="cmd-k-button"
+    class="fixed-btn cmd-k-btn no-print has-tooltip"
+    aria-label="{{.UI.CmdK.Button.AriaLabel}}"
+    data-tooltip="{{.UI.CmdK.Button.Tooltip}}"
+    _="on click set #cmd-k-bar's @open to true">
+    <iconify-icon icon="mdi:text-box-search-outline"></iconify-icon>
+</button>
+{{end}}