BIT-440: wire routing defaults into Ready-gate automation

[cjarguello]

Supersedes closed stacked PR #100 after #97 merged and its base branch was deleted.

Goal

• Wire routing defaults from linear/contracts/linear_type_classifier_v1.json into automation where safe.
• No PM/QA skip without classifier intake evidence.

What this PR does

• On Ready-gate pass, the engine computes the routing recommendation via classify_route(...) and posts a comment with QA/PM recommendation + reason.
• Safe automation: if route says QA=skip (currently only the Design rule), the engine sets QA Review=qa-skipped automatically, backed by explicit classifier intake.
• PM routing remains advisory-only (no automatic pm-skipped).

CJ Admin authorization

• Force merge / QA skip authorized in thread.

Validation

• python3 -m json.tool linear/contracts/linear_type_classifier_v1.json >/dev/null
• python3 -m unittest linear.tests.test_engine linear.tests.test_classifier_corrections
• git diff --check