docs: add the docs guide (quickstart, connect, api, concepts)

Docs in the nav pointed at the bare /endpoints reference, not a guide. Adds
/docs in the calm constellation theme with a sidebar over four sections:
quickstart (the real self-host steps plus the hosted waitlist), connect your
agent (the shared snippets, identical to onboarding, plus the REST shape), an
organized API reference of the routes that exist, and a plain-language
how-it-works covering importance/confidence/recency, the active/settling/
resting tiers, the relation graph, and the adversarially tested isolation. The
full per-endpoint reference stays at /endpoints and is linked from the sidebar.
Landing Docs and Read the docs CTAs now point at /docs.

Author: guirguispierre

mockup/shots/docs-1280-api.png

@@ -41,6 +41,7 @@ import {
   deployHtml,
   deployScript,
   handleApiWaitlist,
+  docsHtml,
   endpointsIndexHtml,
   mcpLandingHtml,
   endpointGuideForPath,
@@ -94,6 +95,12 @@ export default {
         });
       }
 
+      if (url.pathname === '/docs') {
+        return new Response(docsHtml(url), {
+          headers: { 'Content-Type': 'text/html; charset=utf-8' },
+        });
+      }
+
       if (url.pathname === '/endpoints') {
         return new Response(endpointsIndexHtml(url), {
           headers: { 'Content-Type': 'text/html; charset=utf-8' },