chore: ZXDB env validation, MySQL setup, API & UI

This sanity commit wires up the initial ZXDB integration and a minimal UI to explore it.

Key changes:
- Add Zod-based env parsing (`src/env.ts`) validating `ZXDB_URL` as a mysql:// URL (t3.gg style).
- Configure Drizzle ORM with mysql2 connection pool (`src/server/db.ts`) driven by `ZXDB_URL`.
- Define minimal ZXDB schema models (`src/server/schema/zxdb.ts`): `entries` and helper `search_by_titles`.
- Implement repository search with pagination using helper table (`src/server/repo/zxdb.ts`).
- Expose Next.js API route `GET /api/zxdb/search` with Zod query validation and Node runtime (`src/app/api/zxdb/search/route.ts`).
- Create new app section “ZXDB Explorer” at `/zxdb` with search UI, results table, and pagination (`src/app/zxdb/*`).
- Add navbar link to ZXDB (`src/components/Navbar.tsx`).
- Update example.env with readonly-role notes and example `ZXDB_URL`.
- Add drizzle-kit config scaffold (`drizzle.config.ts`).
- Update package.json deps: drizzle-orm, mysql2, zod; devDeps: drizzle-kit. Lockfile updated.
- Extend .gitignore to exclude large ZXDB structure dump.

Notes:
- Ensure ZXDB data and helper tables are loaded (see `ZXDB/scripts/ZXDB_help_search.sql`).
- This commit provides structure-only browsing; future work can enrich schema (authors, labels, publishers) and UI filters.

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

src/env.ts

@@ -0,0 +1,33 @@
+import { z } from "zod";
+
+// Server-side environment schema (t3.gg style)
+const serverSchema = z.object({
+  // Full MySQL connection URL, e.g. mysql://user:pass@host:3306/zxdb
+  ZXDB_URL: z
+    .string()
+    .url()
+    .refine((s) => s.startsWith("mysql://"), {
+      message: "ZXDB_URL must be a valid mysql:// URL",
+    }),
+});
+
+function formatErrors(errors: z.ZodFormattedError<Map<string, string>, string>) {
+  return Object.entries(errors)
+    .map(([name, value]) => {
+      if (value && "_errors" in value) {
+        return `${name}: ${(value as any)._errors.join(", ")}`;
+      }
+      return `${name}: invalid`;
+    })
+    .join("\n");
+}
+
+const parsed = serverSchema.safeParse(process.env);
+if (!parsed.success) {
+  // Fail fast with helpful output in server context
+  // eslint-disable-next-line no-console
+  console.error("❌ Invalid environment variables:\n" + formatErrors(parsed.error.format()));
+  throw new Error("Invalid environment variables");
+}
+
+export const env = parsed.data;