test: make unknown-business-status harness tmux-independent

[Florious95]

Owns the Grok Bot-only Harvest2 red and the v0.5.69 MCP harness regression introduced by this PR.

Root causes:

• Harvest2 T3 used the full tmux fixture even though it only tests stdio ingress.
• While splitting that fixture, the shared nested task_mcp row was accidentally given result_route=pipeline. That changed the default report_result contract and made the leader-visible canary count zero.

Changes:

• Keep Harvest2 T3 on the tmux-independent fixture.
• Preserve task_mcp default leader routing in the shared pane-delivery fixture.

Validation at head a5605ca:

• cargo test -p team-agent --test mcp_simulated_worker_source_red mcp_worker_report_result_is_leader_visible_once_not_queued_only -- --exact --test-threads=1 --nocapture: 1 passed.
• cargo test -p team-agent --lib t3_unknown_business_status_is_preserved_without_normalized_event -- --test-threads=1 --nocapture: 1 passed.
• Grok Linux direct clone, Rust/Cargo 1.95.0, exact MCP selector: 1 passed, ExecMainStatus=0, unit gb-a5605ca8-v0569-mcp-linux-fixed-sol-a1.

Base: five-provider-PR stack head 7e2c65d. No product behavior, timeout, retry, or serialization changed.