test(orchestration): add direct SC-4/SC-9 assertions for Mode-1 recovery

[bug-ops]

Summary

• Adds two direct unit tests closing a transitive-only coverage gap for spec-075 §7 success criteria SC-4 and SC-9, flagged during review of Implement: orchestration node control parity (per-task run_timeout + Mode-1 recovery) #6243/orchestration: /plan confirm gives no user-visible signal when verification judges plan output incomplete #6265 and deliberately deferred to avoid scope creep.
• SC-4 (test_build_prompt_includes_mode1_recovered_state_injection, zeph-orchestration): drives Mode-1 recovery end-to-end (propagate_failure → try_recover) and asserts the injected state_injection value actually reaches build_task_prompt() for a downstream dependent, without leaking the internal __recovery__ completion marker.
• SC-9 (finalize_plan_execution_recovery_derived_task_counted_in_tasks_completed, zeph-core): asserts a __recovery__-derived Completed task is counted by finalize_plan_completed's generic, status-based tasks_completed counter, with a sibling Failed task confirmed excluded for real contrast.
• No production code changes — both mechanisms already behaved correctly; this closes the direct-assertion gap only.

Closes #6301

Test plan

• cargo nextest run -p zeph-orchestration --features llm-planning -E 'test(test_build_prompt_includes_mode1_recovered_state_injection)'
• cargo nextest run -p zeph-core --features scheduler -E 'test(finalize_plan_execution_recovery_derived_task_counted_in_tasks_completed)'
• cargo +nightly fmt --check
• cargo clippy --profile ci --workspace --all-targets --features "desktop,ide,server,chat,pdf,scheduler,testing" -- -D warnings
• cargo nextest run --config-file .github/nextest.toml --workspace --features "desktop,ide,server,chat,pdf,scheduler" --lib --bins — 13812 passed, 0 failed
• RUSTFLAGS="-D warnings" RUSTDOCFLAGS="--deny rustdoc::broken_intra_doc_links" cargo doc --no-deps --workspace --features "desktop,ide,server,chat,pdf,scheduler"
• gitleaks protect --staged --no-banner --redact