feat: initial HELIX scaffold — R&D showcase platform

SvelteKit 2 + Svelte 5 + TypeScript site. SQLite via Drizzle. Gitea OAuth
for authoring (RnD org-gated). Pure SVG + CSS DNA helix on landing.

What lands
- Landing hero with animated two-strand SVG helix + tagline
- /projects + /projects/[slug] (markdown body, dashboard embed allowlist)
- /posts + /posts/[slug]
- Auth-gated /projects/new + /posts/new forms
- Gitea OAuth flow (state, code exchange, org-membership check, sessions)
- Sliding-window cookie sessions (SHA-256 hashed token storage)
- Dockerfile + docker-compose with named-volume SQLite
- Idempotent seed (EVOLV + HELIX projects, welcome post)

Stack notes
- Tailwind v3 (Node 18 compat; v4 needs Node 20+)
- drizzle-orm 0.45+ (patched, no SQL-identifier escape vuln)
- marked for markdown; iframe embeds gated by DASHBOARD_ALLOWED_HOSTS

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/posts/[slug]/+page.svelte

@@ -0,0 +1,84 @@
+<script lang="ts">
+  let { data } = $props();
+  const published = $derived(
+    data.post.publishedAt
+      ? new Date(data.post.publishedAt).toLocaleDateString('en-GB', {
+          day: 'numeric',
+          month: 'long',
+          year: 'numeric'
+        })
+      : ''
+  );
+</script>
+
+<svelte:head>
+  <title>{data.post.title} · HELIX</title>
+  <meta name="description" content={data.post.summary || data.post.title} />
+</svelte:head>
+
+<article class="post">
+  <header class="head">
+    <a href="/posts" class="back">← Posts</a>
+    <h1>{data.post.title}</h1>
+    <div class="meta">
+      {#if data.author}
+        <span class="author">
+          {#if data.author.avatarUrl}
+            <img src={data.author.avatarUrl} alt="" />
+          {/if}
+          {data.author.name ?? data.author.username}
+        </span>
+        <span class="dot">·</span>
+      {/if}
+      <time>{published}</time>
+    </div>
+  </header>
+
+  <div class="prose-helix">
+    {@html data.bodyHtml}
+  </div>
+</article>
+
+<style>
+  .post {
+    max-width: 700px;
+    margin: 0 auto;
+    padding: 3rem 1.5rem 2rem;
+  }
+  .head {
+    margin-bottom: 2rem;
+  }
+  .back {
+    color: var(--color-helix-ink-dim);
+    text-decoration: none;
+    font-size: 0.875rem;
+  }
+  .back:hover {
+    color: var(--color-helix-accent);
+  }
+  h1 {
+    margin: 1rem 0 0.5rem;
+    font-size: clamp(1.8rem, 4.5vw, 2.6rem);
+    font-weight: 700;
+    letter-spacing: -0.02em;
+    line-height: 1.15;
+  }
+  .meta {
+    display: inline-flex;
+    align-items: center;
+    gap: 0.5rem;
+    font-size: 0.85rem;
+    color: var(--color-helix-ink-faint);
+  }
+  .author {
+    display: inline-flex;
+    align-items: center;
+    gap: 0.4rem;
+  }
+  .author img {
+    width: 22px;
+    height: 22px;
+    border-radius: 50%;
+    border: 1px solid var(--color-helix-border);
+  }
+</style>