refactor inconsistent meta route paths and filenames for ensnode-api

[notrab]

In #1672 @lightwalker-eth made the following comment.

We should look to rename this file and follow the consistency of other routes.

For example, some actions to take next:

1. ensnode-api.routes.ts -> meta-api.routes.ts
2. New meta-api.ts extracts the config and indexing-status handlers from ensnode-api.ts into their own module, following the same pattern as resolution-api.ts, name-tokens-api.ts, etc.
3. ensnode-api.ts is now purely a routing hub that mounts sub-APIs. The meta handlers are mounted via app.route("/", metaApi) so URLs (/api/config, /api/indexing-status) remain unchanged.
4. stub-routes.ts updates import from ensnode-api.routes to meta-api.routes.

[coderabbitai]

🔗 Related PRs

#1554 - ENS Referrals API Versioning [merged]
#1636 - refactor(ensnode-sdk): move ENSNodeClient into ENSApi module [merged]
#1661 - feat: zod-openapi for amirealtime-api [merged]

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