Pin clear3's shipped signed-context routing with a baseline test

[thedavidmeister]

Baseline step for #2850: the shipped clear3 routing (alice's eval receives bobSignedContext, bob's receives aliceSignedContext, RaindexV6.sol:705-720) is currently asserted by no test — RaindexV6.clear.context.t.sol passes new SignedContextV1[](0) on both sides.

Add coverage that pins the CURRENT behavior as the baseline:

• A clear context test passing two distinct, distinguishable signed context arrays (different signers and payloads) and asserting exactly which order's evaluation sees which — asserted from inside the evals via signer and content rows, not just non-revert.
• The test documents that it pins shipped V6 behavior (the counterparty-swapped routing), so the future corrected version (clear3 cross-wires alice/bob signed context vs its interface docs; next version must fix it with a loud break #2850's loud break) changes this test deliberately and visibly rather than discovering the routing was never pinned.
• Zero-length and one-sided arrays covered as well (only alice provides context / only bob does), since the swap is only observable when the sides differ.

🤖 Generated with Claude Code

[linear]

RAI-2160