docs: add SolidRPC node provider

[DamianFigiel]

Summary

Adds SolidRPC to the Unichain node provider directory.

The entry lists authenticated HTTPS access for Unichain Mainnet, with upstream routing, failover, monitoring, and recovery handled behind a single integration.

The introductory callout was also clarified because provider capabilities vary and SolidRPC does not advertise WebSocket support.

Type of change

• Fix (typo, broken link, incorrect or outdated content)
• New content (guide, page, code example)
• Update to existing content
• Other

How has this been verified?

• Confirmed the SolidRPC documentation and network catalog are publicly accessible
• Confirmed Unichain appears in the SolidRPC network catalog
• Ran git diff --check

Applicable screenshots

Not applicable — documentation-only provider entry.

Anything else reviewers should know?

The entry lists Unichain Mainnet only. It does not claim Unichain Sepolia, public keyless, or WebSocket support.

[github-actions]

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[github-actions]

Flagging for human verification: this introduces a new, previously-unlisted third-party domain (solidrpc.io) into the docs, including a live link a reader could click to send traffic/credentials to it. I wasn't able to fetch the site in this sandbox to confirm it's a legitimate, operational RPC provider with real Unichain support (vs. a placeholder/parked domain or promotional listing). Before merging, please have a maintainer independently confirm:

• solidrpc.io resolves and is operated by a real RPC service
• solidrpc.io/docs and solidrpc.io/docs/networks exist and actually list Unichain Mainnet
• The service doesn't overlap with an existing spam-listing pattern seen in other provider-directory PRs

No contract addresses or chain IDs are affected, but new external domains added to official docs warrant the same scrutiny.

[github-actions]

Review summary

Small, self-contained content change to content/unichain/tools/node-providers.mdx:

• Adds a new SolidRPC entry, matching the existing structure/format used by other providers (heading, description, "get started" link, ### Supported networks list).
• Updates the intro <Callout> from "All third-party node providers listed below support WebSocket connections" to a more accurate "providers may offer additional method support, higher limits, archive access, or WebSocket connections — check each provider's docs." This is a good correction since it was already inaccurate for other listed providers that don't advertise WebSocket support (e.g. Chainstack, dRPC), and it stays consistent with the PR's claim that SolidRPC itself doesn't support WebSocket.
• No contract addresses, chain IDs, or code samples are touched.
• MDX/heading structure and markdown formatting look valid and consistent with sibling entries; no broken anchors.

One item worth a maintainer's eye (left as an inline comment): this PR adds a brand-new, previously-unlisted domain (solidrpc.io) to the docs. I couldn't fetch external URLs from this sandboxed review environment, so I can't independently confirm the site is a legitimate, operational RPC provider with real Unichain support rather than a promotional/placeholder listing. Recommend a quick manual check of solidrpc.io, solidrpc.io/docs, and solidrpc.io/docs/networks before merge.

Otherwise this looks like a clean, low-risk documentation update.