Keep local pre-push gate output machine-clean

The ROADMAP #694 local pre-push gate should catch stale Rust build breakage without polluting stdout that callers may reserve for structured output. Route the roadmap ID pre-check through stderr like the build gate messages.

Constraint: ROADMAP #693-#695 verification already covers typed analog phase errors, the cargo build gate, and startup preflight warnings; this change only fixes the failing pre-push hook contract found during G013 validation.
Rejected: Reworking hook installation or branch-protection policy | outside the local repository change surface available from this worktree.
Confidence: high
Scope-risk: narrow
Directive: Keep pre-push status/progress output on stderr so stdout stays available for machine callers.
Tested: python3 -m pytest tests/test_pre_push_hook_contract.py -q; cargo test --manifest-path rust/Cargo.toml -p claw-analog rag_response -- --nocapture; cargo test --manifest-path rust/Cargo.toml -p runtime startup_preflight -- --nocapture; python3 scripts/validate_cc2_board.py --board .omx/cc2/board.json; cargo fmt --manifest-path rust/Cargo.toml --all -- --check; cargo build --manifest-path rust/Cargo.toml --workspace --locked
Not-tested: full cargo test --workspace

.github/hooks/pre-push

@@ -13,7 +13,7 @@ cd "$repo_root"
 
 if [[ -x scripts/roadmap-check-ids.sh ]]; then
   echo "pre-push: scripts/roadmap-check-ids.sh" >&2
-  scripts/roadmap-check-ids.sh
+  scripts/roadmap-check-ids.sh >&2
 fi
 
 if [[ "${SKIP_CLAW_PRE_PUSH_BUILD:-}" == "1" ]]; then