feat: core layout, UI atoms, homepage + behaviour modules

- UI atoms: Chip, Button, SplitCvButton, LangSwitch, ThemeToggle, Card,
  SectionLabel, TraceMotif, FramedImage
- core: Base/Seo/Header/MobileNav/Footer/HintBar/SkipLink/ThemeScript
- homepage sections: Hero, ProofStrip, SkillsGrid, ProjectCards,
  ExperienceTimeline, AboutTeaser, ContactBand + Homepage composition (EN/NO)
- behaviour modules: theme, nav (overlay/hint/copy/header), observer (reveal/spy),
  lightbox, form — progressive enhancement, fail-silent
- SEO head component: meta, hreflang from slug map, JSON-LD, OG references
- move content data to src/data (avoid Astro reserved content-collection folder)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

site/src/components/core/ThemeScript.astro

@@ -0,0 +1,21 @@
+---
+/*
+  No-flash theme init. Runs before paint, sets data-theme from stored preference
+  or system (ANIMATION_SPEC — the one permitted inline script; CSP-hashed at the
+  nginx layer). First visit follows the system; once set, the choice persists.
+*/
+---
+
+<script is:inline>
+  (function () {
+    try {
+      var t = localStorage.getItem('theme');
+      if (t !== 'light' && t !== 'dark') {
+        t = window.matchMedia('(prefers-color-scheme: light)').matches ? 'light' : 'dark';
+      }
+      document.documentElement.dataset.theme = t;
+    } catch (e) {
+      document.documentElement.dataset.theme = 'dark';
+    }
+  })();
+</script>