fix: user-defined plural interfaces now take priority over auto-generated plural routes

[Many0nne]

Description:

Problem

When a user explicitly defined a plural interface (e.g., Users) alongside its singular counterpart (User), two bugs

occurred:

Routing (findTypeForUrl):
URL /users was always singularized to "user" → "User" before the typeMap lookup. This made any user-defined plural
interface (e.g., Users) permanently unreachable — the router would never match it regardless of its definition.

OpenAPI spec (generateOpenAPISpec):
Both User and Users would independently generate a path for /users. The result was order-dependent: whichever
interface was processed last would overwrite the other's definition in the spec.

Fix

src/utils/typeMapping.ts — findTypeForUrl:
Before falling back to singularization, the function now checks whether the PascalCase form of the URL segment (e.g.,
"Users" from /users) exists directly in the typeMap. If it does, that interface is used as-is with isArray: false,
honoring the user's explicit definition.

src/core/swagger.ts — generateOpenAPISpec:
When auto-generating the plural path for a singular interface (e.g., /users for User), the function now skips that
generation if a corresponding user-defined plural interface (e.g., Users) is already present in the typeMap. The
explicit interface's own path generation handles it instead.

Behavior after fix

TypeMap contains	GET /users	GET /user
User only	Array of User	Single User
Users only	Single Users	404
User + Users	Single Users (user wins)	Single User