feat(themes): Add AE_Firefly variant themes — SteelBlue, Indigo, Rainbow

Three new Firefly-family themes following the AE_Firefly design system:
- AE_Firefly_SteelBlue: metallic steel blue primary (~214°), burnished gold
  secondary, cobalt navy tertiary, chrome silver surfaces
- AE_Firefly_Indigo: deep indigo primary (~266°), violet secondary, dusty
  rose tertiary, velvet slate surfaces
- AE_Firefly_Rainbow: coral-red primary (~15°), emerald green secondary,
  rich violet tertiary, sunrise cream surfaces (spans the visible spectrum)

All variants share consistent semantic colors (success/warning/error) with
AE_Firefly for cross-theme recognizability. All WCAG 2.1 AA compliant.

Also adds URL param support for theme switching:
- ?theme=AE_Firefly_SteelBlue&theme_mode=dark
- Params applied to ae_loc (persisted), then silently removed via replaceState

src/lib/app_components/e_app_theme.svelte

@@ -101,6 +101,10 @@ if ($ae_loc.app_cfg.theme_mode == 'light') {
             <!-- <option value="ae_c_osit">OSIT</option> -->
             <option value="AE_OSIT_default">OSIT</option>
             <option value="AE_Firefly">Firefly ✦</option>
+            <option value="AE_Firefly_SteelBlue">Firefly SteelBlue ✦</option>
+            <option value="AE_Firefly_Indigo">Firefly Indigo ✦</option>
+            <option value="AE_Firefly_Rainbow">Firefly Rainbow ✨</option>
+            <!-- <option value="AE_Firefly_new-name">Firefly new-name ✦</option> -->
             <option value="AE_c_IDAA_light">IDAA - light</option>
             <option value="AE_c_LCI">LCI</option>
         </select>