feat(isabelle-edits): Clarify theme structure and add SVG icon support

Improves theme organization by adopting a 7-in-1 SCSS structure.

Introduces support for SVG icons within templates, enhancing visual flexibility.

Adds a checkmark SVG asset.

falcon/modules/is_searchbar/views/templates/hook/is_searchbar.tpl

@@ -9,7 +9,12 @@
 					   name="s"
 					   value="{$search_string}">
 				<button type="submit" class="search-form__btn btn">
-					<span class="material-icons">search</span>
+                    {capture name="svg_output"}{svg_icon file='search.svg'}{/capture}
+                    {if $smarty.capture.svg_output}
+                        {$smarty.capture.svg_output nofilter}
+                    {else}
+                        <span class="header-top__icon material-icons">search</span>
+                    {/if}
 				</button>
 			</div>
 		</form>