Sami/update testnet explorer

[0xSami-m]

blockscout testnet explorer is being deprecated on Jul 10 so I've replaced mentions of it with the etherscan explorer

[claude]

⚠️ 1 finding

• Summary: replaces one testnet Blockscout reference with a new testnet_etherscan var, in advance of the 2026-07-10 Blockscout deprecation.
• Inline comments: 1 anchorable finding on the new vars.yaml entry, covering all still-unmigrated call sites.
• Body-only items: none.

Still open from earlier reviews: none (first review).

[claude]

[Major] The PR description says all mentions of the deprecating testnet Blockscout have been replaced, but only one call site (docs/user/get-started.md) was updated. With Blockscout deprecation on 2026-07-10 (8 days out), the following references will become broken links immediately after that date:

• docs/user/connect.md:87 — wallet setup table still uses space.vars.testnet_blockscout.
• docs/user/connect.md:112 — the "Block Explorers → Testnet" tab lists only Blockscout; consider replacing with Etherscan (and/or adding Etherscan alongside).
• docs/user/force-inclusion.md:101 — hardcoded megaeth-testnet-v2.blockscout.com.
• docs/dev/bridge-erc20.md:139 — hardcoded testnet Blockscout URL in the "track the L2 deposit" hint.
• docs/dev/send-tx/contracts.md:20-22 — testnet token address links (MEGA, WETH, Multicall3) hardcoded to megaeth-testnet-v2.blockscout.com.

Please either update these to space.vars.testnet_etherscan / https://testnet-mega.etherscan.io in the same PR, or explicitly scope the PR title/description to "only the get-started page" so reviewers know Blockscout links elsewhere remain intentional. Leaving testnet_blockscout in vars.yaml is fine if the deprecating URL still resolves during a transition window, but any page still resolving that var after 2026-07-10 will render a dead link.