docs: add ZXDB guide; refresh README & AGENTS

Expand and update documentation to reflect the current app (Registers + ZXDB Explorer), with clear setup and usage instructions.

Changes
- README: add project overview including ZXDB Explorer; routes tour; ZXDB setup (DB import, helper search tables, readonly role); environment configuration; selected API endpoints; implementation notes (Next 15 async params, Node runtime for mysql2, SSR/ISR usage); links to AGENTS.md and docs/ZXDB.md.
- docs/ZXDB.md (new): deep-dive guide covering database preparation, helper tables, environment, Explorer UI, API reference under /api/zxdb, performance approach (helper tables, parallel queries, ISR), troubleshooting, and roadmap.
- AGENTS.md: refresh Project Overview/Structure with ZXDB routes and server/client boundaries; document Next.js 15 dynamic params async pattern for pages and API routes; note Drizzle+mysql2, Node runtime, and lookup `text`→`name` mapping; keep commit workflow guidance.
- example.env: add reference to docs/ZXDB.md and clarify mysql:// format and setup pointers.

Notes
- Documentation focuses on the current state of the codebase (what the code does), not a log of agent actions.
- Helper SQL at ZXDB/scripts/ZXDB_help_search.sql is required for performant searches.

Signed-off-by: Junie@lucy.xalior.com

src/app/zxdb/languages/page.tsx

@@ -1,11 +1,15 @@
-import LanguageList from "./LanguageList";
-import { listLanguages } from "@/server/repo/zxdb";
+import LanguagesSearch from "./LanguagesSearch";
+import { searchLanguages } from "@/server/repo/zxdb";
 
 export const metadata = { title: "ZXDB Languages" };
 
-export const revalidate = 3600;
+// Depends on searchParams (?q=, ?page=). Force dynamic so each request renders correctly.
+export const dynamic = "force-dynamic";
 
-export default async function Page() {
-  const items = await listLanguages();
-  return <LanguageList items={items as any} />;
+export default async function Page({ searchParams }: { searchParams: Promise<{ [key: string]: string | string[] | undefined }> }) {
+  const sp = await searchParams;
+  const q = (Array.isArray(sp.q) ? sp.q[0] : sp.q) ?? "";
+  const page = Math.max(1, Number(Array.isArray(sp.page) ? sp.page[0] : sp.page) || 1);
+  const initial = await searchLanguages({ q, page, pageSize: 20 });
+  return <LanguagesSearch initial={initial as any} initialQ={q} />;
 }