feat: add subdomain-based site context with SSR resolution

Resolve the active site from the request Host header on the server and
expose it through a SiteContext provider so the app can vary rendering
per subdomain. Serialize the resolved site into the document shell
(data-site attribute + window.__SITE__) so client hydration matches the
server render. Add host-based Vercel rewrites mapping each subdomain to
its site root, and include unit tests for the site resolution logic.

src/lib/site-context.ts

@@ -0,0 +1,171 @@
+/**
+ * Shared site definitions and host-to-site resolver.
+ *
+ * Pure module — intentionally imports NO env / server-only code — so it is
+ * safe to import from both server and client (and from unit tests).
+ *
+ * This is the keystone of the subdomain-routing feature (task 01). Every
+ * content task (05-11) consumes `SITE_CONFIG` metadata via `useSite()`,
+ * and the server-side host detection in
+ * `src/server/site-context-server.ts` builds on `resolveSiteFromHost`.
+ */
+
+export type SiteId = "main" | "nessa" | "lineage" | "gaze" | "inputhalo";
+
+export interface Site {
+  /** Canonical id, also serialized into `<html data-site>` and `window.__SITE__`. */
+  id: SiteId;
+  /** Subdomain label, e.g. `"nessa"`. Empty string for the main site. */
+  subdomain: string;
+  /** Fully-qualified domain, e.g. `"nessa.freno.me"`. `"freno.me"` for main. */
+  domain: string;
+  /**
+   * Internal route prefix the vercel.json host rewrite targets. SolidStart
+   * file-routing places subdomain pages under `src/routes/<prefix>/*`.
+   * Empty string for main.
+   */
+  baseRoutePrefix: string;
+  /** Human-friendly brand / product name. */
+  displayName: string;
+  /** Appended to page titles, e.g. `" | Nessa"`. */
+  titleSuffix: string;
+  /** Hex brand color used for theming accents / OG image backgrounds. */
+  brandColor: string;
+  /** Default OpenGraph image path (resolved against the site root). */
+  ogDefaultImage: string;
+  /** Favicon path for this site. */
+  faviconPath: string;
+}
+
+export const SITE_CONFIG: Record<SiteId, Site> = {
+  main: {
+    id: "main",
+    subdomain: "",
+    domain: "freno.me",
+    baseRoutePrefix: "",
+    displayName: "Michael Freno",
+    titleSuffix: " | Michael Freno",
+    brandColor: "#89b4fa",
+    ogDefaultImage: "/blueprint.jpg",
+    faviconPath: "/favicon.ico"
+  },
+  nessa: {
+    id: "nessa",
+    subdomain: "nessa",
+    domain: "nessa.freno.me",
+    baseRoutePrefix: "/nessa",
+    displayName: "Nessa",
+    titleSuffix: " | Nessa",
+    brandColor: "#cba6f7",
+    ogDefaultImage: "/nessa/og-default.png",
+    faviconPath: "/nessa/favicon.ico"
+  },
+  lineage: {
+    id: "lineage",
+    subdomain: "lineage",
+    domain: "lineage.freno.me",
+    baseRoutePrefix: "/lineage",
+    displayName: "Life and Lineage",
+    titleSuffix: " | Life and Lineage",
+    brandColor: "#a6e3a1",
+    ogDefaultImage: "/lineage/og-default.png",
+    faviconPath: "/lineage/favicon.ico"
+  },
+  gaze: {
+    id: "gaze",
+    subdomain: "gaze",
+    domain: "gaze.freno.me",
+    baseRoutePrefix: "/gaze",
+    displayName: "Gaze",
+    titleSuffix: " | Gaze",
+    brandColor: "#f9e2af",
+    ogDefaultImage: "/gaze/og-default.png",
+    faviconPath: "/gaze/favicon.ico"
+  },
+  inputhalo: {
+    id: "inputhalo",
+    subdomain: "inputhalo",
+    domain: "inputhalo.freno.me",
+    baseRoutePrefix: "/inputhalo",
+    displayName: "InputHalo",
+    titleSuffix: " | InputHalo",
+    brandColor: "#f38ba8",
+    ogDefaultImage: "/inputhalo/og-default.png",
+    faviconPath: "/inputhalo/favicon.ico"
+  }
+};
+
+/** Ordered subdomain sites used for host matching. */
+const SUBDOMAIN_SITES: ReadonlyArray<Site> = [
+  SITE_CONFIG.nessa,
+  SITE_CONFIG.lineage,
+  SITE_CONFIG.gaze,
+  SITE_CONFIG.inputhalo
+];
+
+const BASE_DOMAIN = "freno.me";
+
+/** Matches `<sub>.localhost` and `<sub>.localhost:<port>` (dev only). */
+const DEV_HOST_RE = /^([a-z0-9-]+)\.localhost$/i;
+
+export const MAIN_SITE: Site = SITE_CONFIG.main;
+
+/**
+ * Resolve a `Site` from a raw `Host` header value (or hostname).
+ *
+ * Handles:
+ *  - exact product subdomains (`nessa.freno.me` → nessa)
+ *  - `www.` prefix (`www.freno.me` → main)
+ *  - the bare apex (`freno.me` → main)
+ *  - port suffixes (`freno.me:3000` → main)
+ *  - localhost dev (`localhost` / `localhost:3000` → main)
+ *  - subdomain dev (`nessa.localhost` / `nessa.localhost:3000` → nessa)
+ *  - unknown hosts / unknown subdomains → main (fail-safe default)
+ *
+ * Pure & synchronous — no I/O, no env access.
+ */
+export function resolveSiteFromHost(host: string | null | undefined): Site {
+  if (!host) return MAIN_SITE;
+
+  // Normalize: trim, lowercase, strip optional `:port` suffix.
+  const normalized = host.trim().toLowerCase().replace(/:\d+$/, "");
+  if (!normalized) return MAIN_SITE;
+
+  // Strip a leading `www.` so `www.freno.me` behaves like `freno.me`.
+  const withoutWww = normalized.replace(/^www\./, "");
+
+  if (withoutWww === BASE_DOMAIN) return MAIN_SITE;
+
+  // Exact subdomain.<base> match.
+  for (const site of SUBDOMAIN_SITES) {
+    if (withoutWww === `${site.subdomain}.${BASE_DOMAIN}`) return site;
+  }
+
+  // Dev pattern: <sub>.localhost[:port] (browsers resolve `*.localhost`).
+  const devMatch = normalized.match(DEV_HOST_RE);
+  if (devMatch) {
+    const sub = devMatch[1]!.toLowerCase();
+    for (const site of SUBDOMAIN_SITES) {
+      if (sub === site.subdomain) return site;
+    }
+    // `localhost` alone or unknown `<x>.localhost` → main.
+    return MAIN_SITE;
+  }
+
+  // Unknown `*.freno.me` (e.g. a future subdomain not yet configured) → main.
+  if (withoutWww.endsWith(`.${BASE_DOMAIN}`)) return MAIN_SITE;
+
+  // Anything else entirely (IPs, foreign hosts) → main as a safe default.
+  return MAIN_SITE;
+}
+
+/**
+ * Resolve the active site from a client `window.location`, used by the
+ * SolidJS `SiteContext` provider during hydration. Server codepaths should
+ * use `getSiteFromEvent` / `getSiteFromRequest` instead.
+ */
+export function resolveSiteFromLocation(
+  hostname: string | null | undefined
+): Site {
+  return resolveSiteFromHost(hostname);
+}