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/login/+page.svelte

@@ -0,0 +1,36 @@
+<script lang="ts">
+  import { SITE } from '$lib/config';
+</script>
+
+<svelte:head>
+  <title>Sign in · {SITE.name}</title>
+</svelte:head>
+
+<section class="mx-auto flex min-h-[70vh] max-w-md flex-col justify-center px-6 py-16">
+  <div class="rounded-2xl border border-helix-border bg-helix-bg-2/60 p-10 backdrop-blur">
+    <h1 class="text-3xl font-semibold tracking-tight">Sign in to {SITE.name}</h1>
+    <p class="mt-3 text-helix-ink-dim">
+      HELIX uses your <strong class="text-helix-ink">Gitea</strong> account at
+      <code class="font-mono text-sm">{SITE.giteaBaseUrl.replace('https://', '')}</code>.
+      Anyone can read; authoring is restricted to the
+      <code class="font-mono text-sm">{SITE.giteaOrg}</code> organisation.
+    </p>
+
+    <a
+      href="/auth/gitea"
+      class="mt-8 inline-flex w-full items-center justify-center gap-3 rounded-lg bg-helix-process px-5 py-3 text-base font-medium text-white shadow-lg shadow-helix-process/30 transition hover:bg-helix-area focus:outline-none focus-visible:ring-2 focus-visible:ring-helix-accent"
+    >
+      <svg viewBox="0 0 24 24" class="h-5 w-5" aria-hidden="true">
+        <path
+          fill="currentColor"
+          d="M12 2a10 10 0 0 0-3.16 19.5c.5.1.68-.21.68-.47v-1.7c-2.78.6-3.37-1.34-3.37-1.34-.45-1.16-1.11-1.47-1.11-1.47-.9-.62.07-.6.07-.6 1 .07 1.52 1.03 1.52 1.03.89 1.52 2.34 1.08 2.91.82.09-.65.35-1.08.63-1.33-2.22-.25-4.56-1.11-4.56-4.94 0-1.09.39-1.99 1.03-2.69-.1-.25-.45-1.27.1-2.65 0 0 .84-.27 2.75 1.02a9.6 9.6 0 0 1 5 0c1.9-1.29 2.74-1.02 2.74-1.02.55 1.38.2 2.4.1 2.65.64.7 1.03 1.6 1.03 2.69 0 3.84-2.34 4.69-4.57 4.94.36.31.68.92.68 1.86v2.76c0 .27.18.58.69.48A10 10 0 0 0 12 2"
+        />
+      </svg>
+      Continue with Gitea
+    </a>
+
+    <p class="mt-6 text-xs text-helix-ink-faint">
+      You'll be redirected to Gitea to approve, then back here. No password is stored by HELIX.
+    </p>
+  </div>
+</section>