Fix e2e smoke realtime and wasm setup

[lukacf]

Linear: https://linear.app/lucrfr/issue/LUC-403/fix-all-e2e-smoke-failures

Summary

• teach the web WASM build to honor RKAT_WASM_PACK_BIN/WASM_PACK and have the BuildBuddy e2e-smoke foundation fetch the pinned wasm-pack binary
• gate realtime SDK smoke scenarios on OpenAI realtime credentials and isolate the TypeScript realtime realm
• make realtime member status assertions tolerate active/unattached channels and disambiguate scenario 71 peer responses by request_subject

Validation

• bash -n scripts/e2e-smoke-lane scripts/buildbuddy-bazel-poc
• node --check sdks/web/scripts/build-wasm.mjs && node --check sdks/typescript/tests/e2e_smoke.test.mjs
• python3 -m py_compile sdks/python/tests/test_e2e_smoke.py
• ./scripts/e2e-smoke-filter --scenario 47/58/59/64/71/72
• make fmt-check
• ./scripts/repo-cargo test -p xtask --test buildbuddy_static_lanes -- --nocapture
• MEERKAT_BUILDBUDDY=1 make check (BuildBuddy invocation c555b0c3-ef97-45c3-b312-d8c5ed6729d4)

Note: MEERKAT_BUILDBUDDY=1 MEERKAT_E2E_EXECUTION_MODE=prebuilt SCENARIO=47 make e2e-smoke built the BuildBuddy foundation and fetched the pinned wasm-pack target, then this Linux workspace hit the expected local platform mismatch executing the macOS arm64 prebuilt e2e_artifacts_bin. BuildBuddy invocation a119c237-3667-49ce-aefb-ebbf06b1bd3e.

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