fix(configurator): centre Process Editor button icon + make icon white

- Icon + label now share an inline-flex row with align-items: center,
  so both sit on the button's vertical midline regardless of line-
  height inheritance.
- Dedicated gap (10px) replaces the me-2 utility so the _hint block's
  .fa { margin-bottom: 16px } can't bleed in and push the icon off.
- Icon colour forced to #ffffff to match the button's white label —
  contrast against btn-primary green is now clean.

fusion_plating_configurator → 19.0.12.3.0

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_configurator/static/src/xml/fp_part_process_composer.xml

@@ -66,9 +66,9 @@
                             <p>This part has a composed process tree. Click below to open the
                             full tree editor where you can add, remove, reorder, and configure
                             the process nodes.</p>
-                            <button class="btn btn-primary"
+                            <button class="btn btn-primary o_fp_part_composer_editor_btn"
                                     t-on-click="() => this.openRecipeEditor()">
-                                <i class="fa fa-sitemap me-2"/>
+                                <i class="fa fa-sitemap"/>
                                 <span>Open Process Editor</span>
                             </button>
                         </div>