feat(llms-txt): add API route for llms.txt generation

Serve llms.txt at /api/registry/llms-txt/[...pkg] following existing
registry API patterns with cached event handler and SWR.

Author: lukeocodes

server/api/registry/llms-txt/[...pkg].get.ts

@@ -0,0 +1,50 @@
+import * as v from 'valibot'
+import { PackageRouteParamsSchema } from '#shared/schemas/package'
+import { CACHE_MAX_AGE_ONE_HOUR } from '#shared/utils/constants'
+import { handleApiError } from '#server/utils/error-handler'
+import { handleLlmsTxt } from '#server/utils/llms-txt'
+
+/**
+ * Serves llms.txt for an npm package — a single LLM-friendly markdown document
+ * aggregating README and agent instruction files (CLAUDE.md, AGENTS.md, etc.).
+ *
+ * URL patterns:
+ * - /api/registry/llms-txt/nuxt              → latest version
+ * - /api/registry/llms-txt/@nuxt/kit         → scoped, latest
+ * - /api/registry/llms-txt/nuxt/v/3.12.0    → specific version
+ * - /api/registry/llms-txt/@nuxt/kit/v/1.0.0 → scoped, specific version
+ */
+export default defineCachedEventHandler(
+  async event => {
+    const pkgParamSegments = getRouterParam(event, 'pkg')?.split('/') ?? []
+    if (pkgParamSegments.length === 0) {
+      throw createError({ statusCode: 404, message: 'Package name is required.' })
+    }
+
+    const { rawPackageName, rawVersion } = parsePackageParams(pkgParamSegments)
+
+    try {
+      const { packageName, version } = v.parse(PackageRouteParamsSchema, {
+        packageName: rawPackageName,
+        version: rawVersion,
+      })
+
+      const content = await handleLlmsTxt(packageName, version)
+      setHeader(event, 'Content-Type', 'text/markdown; charset=utf-8')
+      return content
+    } catch (error: unknown) {
+      handleApiError(error, {
+        statusCode: 502,
+        message: 'Failed to generate llms.txt.',
+      })
+    }
+  },
+  {
+    maxAge: CACHE_MAX_AGE_ONE_HOUR,
+    swr: true,
+    getKey: event => {
+      const pkg = getRouterParam(event, 'pkg') ?? ''
+      return `llms-txt:${pkg.replace(/\/+$/, '').trim()}`
+    },
+  },
+)