Flatten the repo: move everything out of app/ to the root

Now that the CLI and the Next.js app are one package, nesting it inside
app/ served no purpose - the repo root itself becomes the published
npm package. Merges app/.gitignore and app/README.md into the root
versions, drops the now-duplicate app/LICENSE, and updates path
references (README, docs/ARCHITECTURE.md, docs/CONFIG_REFERENCE.md,
package.json's repository.directory) that assumed the app/ nesting.

Also fixes a real bug this surfaced: the in-app docs viewer resolved
docs/ relative to process.cwd(), which only worked by accident when the
CLI happened to be invoked from app/'s parent directory. A first attempt
at fixing it with import.meta.dirname broke instead, for the same
cross-module-graph reason config-path resolution already documented -
Next compiles Route Handlers through a separate module graph that
doesn't preserve source-relative import.meta paths. Fixed by exposing
the app root via TRIGGERSHELL_APP_ROOT (set once in server.ts, where
import.meta *does* resolve correctly), the same pattern already used
for TRIGGERSHELL_CONFIG_PATH.

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

src/app/(app)/docs/[slug]/page.tsx

@@ -0,0 +1,41 @@
+export const dynamic = "force-dynamic";
+
+import type { Metadata } from "next";
+import Link from "next/link";
+import { notFound } from "next/navigation";
+import { ArrowLeft } from "lucide-react";
+import { getDocMeta, readDocContent } from "@/lib/docs";
+import { MarkdownViewer } from "@/components/docs/markdown-viewer";
+
+interface DocPageProps {
+  params: Promise<{ slug: string }>;
+}
+
+export async function generateMetadata({
+  params,
+}: DocPageProps): Promise<Metadata> {
+  const { slug } = await params;
+  return { title: getDocMeta(slug)?.title ?? "Doc not found" };
+}
+
+export default async function DocPage({ params }: DocPageProps) {
+  const { slug } = await params;
+  const doc = getDocMeta(slug);
+  if (!doc) notFound();
+
+  const content = readDocContent(doc);
+  if (content === null) notFound();
+
+  return (
+    <div className="mx-auto flex max-w-3xl flex-col gap-6">
+      <Link
+        href="/docs"
+        className="text-muted-foreground hover:text-foreground flex w-fit items-center gap-1 text-sm"
+      >
+        <ArrowLeft className="size-3.5" />
+        All docs
+      </Link>
+      <MarkdownViewer content={content} />
+    </div>
+  );
+}