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/theme/typography.css

@@ -0,0 +1,40 @@
+/* Australis Skyfall — Typography tokens */
+
+:root {
+  /* Families */
+  --font-display: "Bespoke Sans", "Avenir Next", "Segoe UI", sans-serif;
+  --font-body: "Supreme", "Helvetica Neue", "Segoe UI", sans-serif;
+  --font-mono: "VictorMono Nerd Font", "SF Mono", "Cascadia Code", monospace;
+
+  /* Scale (web-app oriented; 14px UI base) */
+  --text-2xs: 11px;
+  --text-xs: 12px;
+  --text-sm: 13px;
+  --text-base: 14px;
+  --text-md: 16px;
+  --text-lg: 18px;
+  --text-xl: 22px;
+  --text-2xl: 28px;
+  --text-3xl: 36px;
+  --text-4xl: 48px;
+  --text-5xl: 64px;
+
+  /* Weights */
+  --weight-regular: 400;
+  --weight-medium: 500;
+  --weight-semibold: 600;
+  --weight-bold: 700;
+  --weight-extrabold: 800;
+
+  /* Line heights */
+  --leading-tight: 1.15;
+  --leading-snug: 1.35;
+  --leading-normal: 1.55;
+  --leading-relaxed: 1.7;
+
+  /* Tracking */
+  --tracking-tight: -0.02em;
+  --tracking-normal: 0;
+  --tracking-wide: 0.06em;
+  --tracking-caps: 0.1em;
+}