restructure routes & conform to zod-openapi spec

[dromzeh]

related to #51 - instead of routes being /v2/asset/upload-asset.ts, we can restructure like so:

/v2/asset/upload/route.ts (logic)
/v2/asset/upload/openapi.ts (openapi definition)
/v2/asset/upload/schema.ts (zod schema)

for routes which require an id or name, we can have /v2/user/get/[name]/route.ts, etc

[dromzeh]

#51