Add a footer and an in-app docs viewer

Footer (in the authenticated app layout, matching where Nav lives):
copyright line, a Docs link, and a link to the project repo.

Docs viewer: /docs lists docs/API.md, CONFIG_REFERENCE.md, and
ARCHITECTURE.md; /docs/[slug] renders one via react-markdown +
remark-gfm (tables, fenced code) inside a Tailwind Typography `prose`
block, dark-mode aware via prose-invert. The markdown files themselves
stay the single source of truth at the repo's docs/ - the app reads
them at request time rather than duplicating their content, resolved
from the app's cwd the same way config paths already are, since a
compiled Route Handler's module graph doesn't preserve source-relative
paths.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/src/components/docs/markdown-viewer.tsx

@@ -0,0 +1,10 @@
+import ReactMarkdown from "react-markdown";
+import remarkGfm from "remark-gfm";
+
+export function MarkdownViewer({ content }: { content: string }) {
+  return (
+    <div className="prose prose-neutral dark:prose-invert max-w-none prose-pre:bg-muted prose-pre:text-foreground">
+      <ReactMarkdown remarkPlugins={[remarkGfm]}>{content}</ReactMarkdown>
+    </div>
+  );
+}