docs(ruby): fix response access pattern + prune phantom destinations

[johnpmitsch]

Summary

Several inaccuracies in the Ruby README caused new users to hit avoidable errors. Found while building a smoke-test suite against the gem.

• Response shape: Document that responses are QuicknodeSdk::IndifferentHash (Hash + Hashie::Extensions::IndifferentAccess). Dot accessors (resp.data.id) don't work — use [] or dig. Added a Response shape section to Language conventions. Fixed the two example blocks (get_rate_limits, get_endpoint_urls) that used dot syntax. Replaced four stale Hashie::Mash mentions with IndifferentHash.
• Pagination key naming: Admin list endpoints return pagination; streams/webhooks return pageInfo (camelCase). Noted explicitly; fixed list_streams Returns line that said page_info.
• update_webhook_template parameters: Accepts only webhook_id, template_args_json, name?, notification_email?. The destination cannot be changed after creation — README previously implied otherwise.
• Postgres destination: Fixed in all four READMEs to table_name/sslmode (matches the wire), not the previously-documented schema/table/use_ssl?. Updated Kafka row with the actual field set.
• Phantom variants: Pruned Mysql, Mongo, Clickhouse, Snowflake, Redis from the destination tables in all four READMEs. These were never in DestinationAttributes — pure phantom documentation.
• eventHashes camelCase: Marked correctly in the evm_contract_events template-args table — the API rejects snake_case.
• rename_tag parameter: Fixed to id: (was documented as tag_id:); added a quick-reference table for the Admin client's delete/rename ID parameters.
• CLAUDE.md: Updated to reflect the actual Ruby response type so future contributors don't repeat the Hashie::Mash mistake.

Docs-only — no code changes.

Test plan

• cargo check && just lint pass locally (verified)
• Skim the four destination tables to confirm they list only Webhook/S3/Azure/Postgres/Kafka
• Skim the Ruby README's new Response shape + Pagination notes and the delete-method quick-reference table
• Spot-check that the example snippets compile/run against the live SDK (e.g. get_endpoint_urls)