fix(docs): add ACP.md frontmatter and flatten docs/meta.json pages format

fumadocs-mdx requires a YAML title in every .md file and does not support
nested object entries in meta.json pages arrays — both were introduced by
PR #3438 and broke the webpack build.

docs/frameworks/ACP.md

@@ -1,3 +1,7 @@
+---
+title: ACP (Agent Client Protocol)
+---
+
 # ACP (Agent Client Protocol)
 
 > **TL;DR**: ACP lets OmniRoute spawn CLI agents (like Claude Code, Codex, Gemini CLI) as child processes instead of using HTTP APIs. This gives you "CLI-as-backend" transport.

docs/meta.json

@@ -1,12 +1,13 @@
 {
   "pages": [
-    {
-      "title": "For Non-Tech Users",
-      "pages": ["getting-started", "guides"]
-    },
-    {
-      "title": "For Tech Users",
-      "pages": ["architecture", "reference", "frameworks", "routing", "security", "compression", "ops"]
-    }
+    "getting-started",
+    "guides",
+    "architecture",
+    "reference",
+    "frameworks",
+    "routing",
+    "security",
+    "compression",
+    "ops"
   ]
 }