fix: #412/#413/#414 runtime stability and PR governance preflight

## #413 — runtime_verify_monitor.sh pipefail fix
- find_live_pids() now captures pgrep output via local variable with || true
  so pipefail never triggers on no-match (pgrep exit 1)
- Regression test added: monitor survives MAX_LOOPS=1 without crash

## #412 — startup crash logging improvement
- Add asyncio.CancelledError catch in sync_positions_from_broker call
  so BaseException-level cancellations are logged before propagating
- Provides evidence in run log if CancelledError causes future startup aborts

## #414 — PR governance preflight
- validate_pr_body.py: add REQ-ID/TASK-ID/TEST-ID pattern checks (--no-governance flag to skip)
- docs/workflow.md: new "PR Governance Preflight (Mandatory)" section
- docs/commands.md: "PR Body Governance Preflight" section before tea pulls create
- Tests: 4 new governance traceability tests in test_validate_pr_body.py

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/runtime_verify_monitor.sh

@@ -36,7 +36,10 @@ check_signal() {
 
 find_live_pids() {
   # Detect live-mode process even when run_overnight pid files are absent.
-  pgrep -af "[s]rc.main --mode=live" 2>/dev/null | awk '{print $1}' | tr '\n' ',' | sed 's/,$//'
+  # Use local variable to avoid pipefail triggering on pgrep no-match (exit 1).
+  local raw
+  raw=$(pgrep -af "[s]rc.main --mode=live" 2>/dev/null) || true
+  printf '%s\n' "$raw" | awk '{print $1}' | tr '\n' ',' | sed 's/,$//'
 }
 
 check_forbidden() {