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/home/SkillsGrid.astro

@@ -0,0 +1,42 @@
+---
+import type { Locale } from '@i18n/locales';
+import { useDict } from '@i18n/t';
+import { homeAnchor } from '@i18n/slugMap';
+import { getSkills } from '@lib/content';
+import SectionLabel from '@components/ui/SectionLabel.astro';
+import Chip from '@components/ui/Chip.astro';
+
+interface Props {
+  locale: Locale;
+}
+const { locale } = Astro.props;
+const d = useDict(locale);
+const groups = getSkills(locale);
+const num = ['01', '02', '03'];
+---
+
+<section id={homeAnchor('skills', locale)} class="mx-auto max-w-[--content-max] px-6 pt-24" data-reveal>
+  <SectionLabel number="01" text={d.home.skillsLabel} />
+  <h2 class="mt-4 text-h2">{d.home.skillsHeading}</h2>
+  <p class="mt-3 max-w-[60ch] text-body text-ink-muted">{d.home.skillsIntro}</p>
+
+  <div class="mt-8 grid gap-5 md:grid-cols-3">
+    {
+      groups.map((group, i) => (
+        <div class="rounded-md border border-line bg-surface-1 p-6 transition-colors duration-[--dur-standard] hover:border-line-strong">
+          <p class="font-mono text-mono-label font-medium uppercase tracking-[0.08em] text-ink-faint">
+            {num[i]} — {group.title}
+          </p>
+          <p class="mt-3 text-small text-ink-muted">{group.context}</p>
+          <ul class="mt-4 flex flex-wrap gap-2">
+            {group.skills.map((s) => (
+              <li>
+                <Chip kind="stack" label={s.name} tooltip={s.tooltip} />
+              </li>
+            ))}
+          </ul>
+        </div>
+      ))
+    }
+  </div>
+</section>