fix(openapi): recursively walk router stack in OpenAPI spec generation (#1441)

[Awosdot]

What changed

• Refactored scripts/generateOpenApi.ts to recursively walk Express Router layers (layer.handle.stack) and flatten nested route mounts[cite: 10].
• Preserved and concatenated URL path prefixes dynamically when traversing sub-routers (e.g., combining /v1 prefix with sub-route paths like /vaults/:id/rebalance)[cite: 10].
• Added unit/contract test coverage by mounting a dummy express.Router with a GET /v1/_test route and validating its inclusion in openapi.json post-generation[cite: 10].
• Regenerated openapi.json and updated snapshot files[cite: 10].

Why

Routes mounted via express.Router without top-level layer.route properties (such as router.use('/v1', v1Router)) were previously omitted during OpenAPI spec generation, preventing SDK validation and leading to undetected API schema drift[cite: 10].

How tested

• Ran npm test and OpenAPI contract test suites to confirm that /v1/_test and all nested routes render correctly in openapi.json[cite: 10].
• Verified that all existing OpenAPI contract tests continue to pass cleanly[cite: 10].

Closes

Closes #1441

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