feat(db): mesh data model — meshes, members, invites, audit log

- pgSchema "mesh" with 4 tables isolating the peer mesh domain
- Enums: visibility, transport, tier, role
- audit_log is metadata-only (E2E encryption enforced at broker/client)
- Cascade on mesh delete, soft-delete via archivedAt/revokedAt

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/db/src/lib/zod.ts

@@ -0,0 +1,6 @@
+import { createSchemaFactory } from "drizzle-zod";
+
+export const { createInsertSchema, createSelectSchema, createUpdateSchema } =
+  createSchemaFactory({
+    coerce: true,
+  });