feat(homepage): Australis Skyfall theme + Arbo-generated aurora background

Replaces the previous theme attempt, which was built on a misread: the ask was
to use Arbo as an IMAGE-GEN ENGINE for the background, with the operator's
Australis Skyfall design system supplying the palette.

theme/ holds the source — colors/layout/typography vendored verbatim from the
Skyfall handoff bundle, Supreme 400/500/700 woff2, the Homepage bindings in
skyfall.css.in, and build.py which inlines fonts + tokens into
conf/custom.css. custom.css is GENERATED; edit the .in file and rebuild.

The build exists because Homepage serves only custom.css and custom.js out of
its config dir, so a @font-face pointing at a vendored woff2 would 404 — the
face has to arrive as a data: URI. The background image takes the other route:
/app/public/images is a real static route, so compose.yaml now mounts
images/ there read-only and settings.yaml points at /images/.

Bindings map Skyfall's semantic layer onto Homepage's DOM: Sea surfaces, the
depth recipe (hairline AND two-layer shadow, never one alone), uppercase
eyebrow group headers, the sanctioned accent-rail on the active tab rather
than a glow, and semantic status colour so a green pill means the service is
actually serving.

Background generated by Arbo (irv-ml1:8201) workflow t2i-ui-background, job
13f0891f4e42, seed 26, flux2-klein-9b, 2048x1152 — abstract, no subject,
cool-temperature aurora. 1.6 MB PNG -> 22 KB WebP.

Two deviations are documented rather than hidden: Skyfall forbids imagery
behind body text (held at opacity 30 as mitigation), and service icons stay
full-colour vendor logos.

NOT DEPLOYED — live still runs the old theme. Prototype on :5199.

stacks/homepage/conf/settings.yaml

@@ -2,11 +2,32 @@
 # https://gethomepage.dev/latest/configs/settings
 title: ... all my base ...
 theme: dark
+# `color:` only accepts Homepage's built-in Tailwind ramps, and none of them is
+# the Skyfall Sea ramp. slate is the nearest cool neutral and acts as the base
+# under conf/custom.css, which is where the real palette lives.
 color: slate
+
+# Background — generated locally, not stock art. Arbo (irv-ml1:8201) rendered
+# it from the `t2i-ui-background` workflow: abstract full-bleed, no subject,
+# aurora blue->cyan->green on near-black, which is the one decorative motif
+# Australis Skyfall permits and its "cool temperature always" imagery rule.
+# Job 13f0891f4e42, seed 26, flux2-klein-9b, 2048x1152.
+#
+# Served from /app/public/images via the read-only mount in compose.yaml —
+# NOT from the config dir, which Homepage will not serve static files out of.
+#
+# ⚠️ opacity is the load-bearing number, not decoration. Skyfall's rule is that
+# the aurora motif never sits behind body text; this dashboard breaks that on
+# purpose, so the image has to stay far enough back that card contrast never
+# suffers. The render is considerably brighter than the "mostly empty" brief,
+# which is exactly what this dials out. Raise it and the cards start fighting
+# the ribbon.
 background:
-  image: https://w.wallhaven.cc/full/p9/wallhaven-p9gr2p.jpg
+  image: /images/skyfall-aurora.webp
   blur: sm
-  opacity: 20
+  saturate: 90
+  brightness: 90
+  opacity: 30
 headerStyle: boxedWidgets
 
 providers: