feat(theme): add AE Firefly theme — 'Shiny serenity, like a firefly.'

New custom Skeleton v4 theme for One Sky IT, LLC.
Design vision: Scott Idem, 2026-03-06.

Color system:
  Primary   — Luminescent teal (bioluminescent shimmer, hue ~184°)
  Secondary — Warm amber-gold (firefly body glow, hue ~90°)
  Tertiary  — Night-sky indigo (depth + serenity, hue ~277°)
  Surface   — Moonlit slate (barely-cool neutral; crisp in light,
              deep midnight in dark)

Section 508 / WCAG 2.1 AA compliance embedded in contrast assignments.
Set as new app default (replacing nouveau).

Files:
  src/ae-firefly.css                        — theme definition
  src/app.css                               — @import registered
  src/lib/app_components/e_app_theme.svelte — 'Firefly ✦' in selector
  src/lib/stores/ae_stores.ts               — default theme_name updated

src/app.css

@@ -27,6 +27,7 @@
 @import './ae-osit-default.css';
 @import './ae-c-lci.css';
 @import './ae-c-idaa-light.css';
+@import './ae-firefly.css';
 
 @source '../node_modules/@skeletonlabs/skeleton-svelte/dist';