feat: add transfer-assets-into-polkadot polkadot-docs test harness

[nhussein11]

Summary

Adds a test harness verifying the Transfer Assets from Ethereum into Polkadot guide. Tests cover getSupportedAssets for Ethereum→AssetHubPolkadot and Ethereum→Hydration routes, the EXTERNAL_CHAINS constant, and EvmBuilder construction; live bridge submission is guarded by it.skipIf(!ETH_PRIVATE_KEY).

Test plan

• cargo fmt --check --package sdk
• cargo clippy --package sdk --locked -- -D warnings
• cargo build --workspace --locked
• Harness tests pass locally (if touched): cd <harness> && npm ci && npm test
• /check-internal-docs passes (if touching versions, docs, badges)
• /branding re-run (if touching .github/brand/tokens.yml or generated assets)
• CI is green on this PR

Checklist

• Branch is NOT master
• Commits follow Conventional Commits (feat:, fix:, chore:, …)
• No secrets, credentials, or .env files committed
• No hardcoded hex colors outside .github/brand/tokens.yml (see DESIGN.md)
• Draft PR if generated by a skill (--draft)

[brunopgalvao]

A few things before this is good to merge:

1. CI uses npm install. Should be npm ci — the harness README tells users npm ci, most sibling polkadot-docs-*.yml workflows do too, and npm install can mutate the lockfile mid-run. One-line fix.

2. Test 4's Hydration branch silently passes. If WETH isn't supported on Hydration, the test bails with a bare return and zero assertions, so it stays green even if the builder breaks. Flip it to it.skipIf(!weth) or assert something before returning.

3. Live test calls .build() but the README says "sign + submit". In most paraspell builders .build() returns the constructed tx without broadcasting. Either the test needs the actual submit method or the README needs to say "build" — please confirm against the SDK and pick one. Right now they're out of sync.

4. @polkadot/api declared but never imported. Drop it from dependencies if it's only there transitively via @paraspell/sdk-pjs, otherwise add the code that uses it. Dead deps just add lockfile noise.

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Style nit (not blocking): await import("ethers") is unnecessary since ethers is a top-level dep — just import it statically at the top of the file. Dynamic imports are for the PAPI-style "load only if used" cases.

Also worth ticking off the test-plan boxes in the PR description as items are verified — per CLAUDE.md they shouldn't ship unchecked.

Happy to approve once 1–4 are sorted.

[brunopgalvao]

All 4 + the style nit addressed cleanly — , on Hydration, README/code aligned on what .build() does, and the unused @polkadot/api drop. CI green. Quick reminder to tick the test-plan boxes in the PR body before merge (CLAUDE.md). Nice work.

[brunopgalvao]

Approved.

Duplicate — body got mangled by shell quoting; superseded by the next approval review with the intended text.