docs(connect-to-base): add Vibenet details and stop linking the unpublished connecting-to-base page

[kriss39]

What changed? Why?

docs/base-chain/quickstart/connecting-to-base.mdx (the page with the Vibenet tab and the "Add to MetaMask" buttons) is in .mintignore, so it never ships; its URL redirects to /get-started/connect-to-base, which only lists Mainnet and Sepolia. Six places still send readers to the old URL for Vibenet-specific instructions, and they all land on a page with no Vibenet on it:

• build-on-base/test-on-vibenet.mdx — "To add Vibenet to your wallet, see Connecting to Base" (plus the Next Steps card)
• specifications/native-account-abstraction.mdx — "learn more in the guide to connecting to vibenet" (with a #vibenet anchor that doesn't exist on the target)
• get-started/base-chain.mdx — the "Connect to Base" card whose copy promises "Base Mainnet, Base Sepolia, or Vibenet"
• base-chain/api-reference/rpc-overview.mdx and specifications/reference/smart-contracts.mdx — generic "network details" links

This PR:

• adds a Vibenet column (RPC https://rpc.vibes.base.org, chain ID 84538453, explorer) to the Network Details table on get-started/connect-to-base, with one sentence on what Vibenet is and a link to Test on Vibenet for the faucet
• repoints the links above to /get-started/connect-to-base (or to /build-on-base/test-on-vibenet where the context is Vibenet itself)

docs.json, .mintignore and the hidden page are untouched; nothing is added to the Get Started tab.

Notes to reviewers

Chain ID checked against the RPC: eth_chainId on https://rpc.vibes.base.org returns 0x509f455 = 84538453, matching build-on-base/test-on-vibenet.

If the plan is to bring the hidden page back (it also carries the MetaMask "add network" buttons), this PR is still a safe interim: the redirect keeps working and the links then just point at the shipped page.

How has it been tested?

node scripts/lint-mdx.js on all six files (the one warning on rpc-overview.mdx:119 is pre-existing), node scripts/validate-docs-structure.js and node scripts/check-terminology.js pass. No remaining links to /base-chain/quickstart/connecting-to-base outside the hidden file itself.

Screenshots

N/A (one extra table column and a sentence; link target changes)

[cb-heimdall]

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