Use FastNear RPC for NEAR by default and accept an RPC URL as the network

[n13]

rpc.mainnet.near.org / rpc.testnet.near.org are deprecated and rate-limit; against mainnet they made transactions expire before broadcast. Every quantus near command that talks to the chain (send, dao, create-account, keys, sign-cold --send) goes through NearRpcClient::for_network, so the change is in one place:

• mainnet → https://rpc.mainnet.fastnear.com, testnet → https://test.rpc.fastnear.com
• --network also accepts an RPC URL directly; --rpc-url still overrides
• README note in the NEAR section

Test covers the two names, a URL as network, --rpc-url precedence and an unknown name. cargo test --lib near::rpc passes, clippy clean.

Replaces the RPC part of #176; the rest of that PR is covered by #174/#175.

[n13]

Reviewer model: GPT-6 Astra

Verdict (advisory): Request changes

Reviewed eb4afb9eedc18bcf575ebd9cc36786842c497a5f against 97b60495905aff0e57398cf1285fe30b568ab547.

[P2] Preserve a canonical network label for cold signing — src/near/rpc.rs:48–49

The newly supported --network https://rpc.mainnet.fastnear.com is accepted by this resolver, but the cold-wallet paths for near send, DAO proposals/votes, and near sign-cold --send pass that same string to sign_transaction_cold. That function calls NearSignRequest::new, whose network allowlist is exactly mainnet/testnet (src/near/cold.rs:157, src/qr/sign_request.rs:114–125). These commands therefore fail before displaying a signing QR with:

NEAR network "https://rpc.mainnet.fastnear.com" is not one of ["mainnet", "testnet"]

I reproduced this against the built PR library: NearRpcClient::for_network(url, None) succeeds, then sign_transaction_cold(..., url, ...) returns that error. Keep URL selection separate from the signing network: either retain URLs exclusively in --rpc-url, or resolve the endpoint's canonical chain label before building the cold-signing request. Add coverage across the resolver/signing boundary; the new resolver-only test misses this failure.

Validation:

• SKIP_CIRCUIT_BUILD=1 cargo test --locked --lib near::: 37 passed.
• SKIP_CIRCUIT_BUILD=1 cargo test --locked --lib qr::sign_request::tests::near_: 4 passed.
• SKIP_CIRCUIT_BUILD=1 cargo build --locked --lib, a standalone cold-signing reproduction, pinned cargo +nightly-2026-08-31 fmt --all -- --check, and git diff --check completed successfully.
• Read-only status and view_account requests succeeded against both new endpoints and reported the intended chains. Endpoint documentation checked: FastNear RPC, NEAR RPC providers.
• GitHub's Linux/macOS build-and-test, format, Clippy/docs, security, and dependency checks passed; Examples was still running at the final check. No transactions were broadcast.

[n13]

Addressed in dc6f9c6: --network now accepts a label or one of its known endpoints (NETWORKS in src/near/rpc.rs: FastNear and rpc.*.near.org for each of mainnet/testnet) and network_label() resolves either to the canonical label. sign_transaction_cold builds the QR request from that label, so the device never sees a URL, and explorer_tx_url resolves the same way. Arbitrary URLs are rejected by --network and belong in --rpc-url. Tests cover the resolver (networks_resolve_to_fastnear_and_known_endpoints_pass_through) and the resolver/signing boundary (known_endpoints_cold_sign_under_their_network_label).

[n13]

Reviewer model: GPT-6 Astra

Verdict (advisory): Approve

Reviewed the full diff at dc6f9c65673a7c50efe9f3f001212cce72163c3a against 97b60495905aff0e57398cf1285fe30b568ab547. The earlier cold-signing blocker is resolved: known endpoints become canonical labels before constructing NearSignRequest, and explorer links use the same resolver. RPC overrides retain precedence. No blocking findings remain.

[P3, non-blocking] Canonicalize the printed near-cli submission hint — src/cli/near.rs:458–460

With near sign-cold --network https://rpc.mainnet.fastnear.com without --send, signing now succeeds, but the suggested submission command still contains network-config https://rpc.mainnet.fastnear.com. near-cli looks up that argument as a configured network name, so the hint fails with a normal configuration. Use network_label(network) here too, producing network-config mainnet. This affects the helper text; the signed output and direct --send path remain usable.

Validation:

• SKIP_CIRCUIT_BUILD=1 cargo test --locked --lib near::: 38 passed, including the new resolver and cold-request regressions.
• SKIP_CIRCUIT_BUILD=1 cargo test --locked --lib qr::sign_request::tests::near_: 4 passed.
• cargo +nightly-2026-08-31 fmt --all -- --check and git diff --check: passed.
• Read-only status and view_account calls succeeded on both defaults; they reported the expected mainnet/testnet chains. Checked endpoint references in FastNear documentation and NEAR's provider list. No transactions were broadcast.
• GitHub Linux build/tests, format, Clippy/docs, security, and dependency checks passed. macOS build/tests and Examples were still running at the final check.