feat(watchdog): proc_blocking alert for orphaned long-lived test processes

Close the observability gap between agent_hung (only tracked jobs by jobs.pid)
and orphaned pytest subprocesses the orchestrator launches itself
(merge_gate.retest_branch / coverage_gate.measure_coverage). On a timeout-kill of
the agent (-9, ORCH-109) the grand-child pytest reparents onto tini and keeps
running for days, starving CPU and failing merge-gate re-test — with no alert.

Strictly inside the observer (watchdog/** + the watchdog compose service):
- watchdog/collectors/proc.py: stdlib-only /proc scan (under pid: host),
  read-only, never-raise -> []; pure parsers split from I/O (tested on a fake
  /proc tree). Never reads /proc/<pid>/environ.
- watchdog/signals.py: pure proc_signals builder, per-entity
  ("proc_blocking", pid), active iff age_s > proc_age_s; actionable RU detail.
- watchdog/core.py: opt-in tick block (gated on proc_enabled -> zero overhead /
  byte-for-byte when off) + RECOVERY synthesis for a vanished process through the
  existing decide()/AlertState (no new anti-spam logic).
- watchdog/config.py: WATCHDOG_PROC_{ENABLED(false),AGE_MIN(60),PATTERNS(pytest),
  COOLDOWN_S(1800)}; default threshold > max(merge_retest_timeout_s=600,
  coverage_run_timeout_s=900) so a legit in-flight run never crosses it.
- docker-compose.yml: pid: host on orchestrator-watchdog ONLY (read-only privilege).

Anti-false-positive and no overlap with agent_hung are by construction (cmdline
scope + age threshold), not fragile cross-namespace PID matching.

Canon synced: WATCHDOG_PROC_* in .env.watchdog.example <-> .env.example block;
documented in LITE_SETUP.md and docs/architecture/README.md (architect). src/**,
/metrics, schema_version, STAGE_TRANSITIONS, QG_CHECKS, check_*, machine-verdict
and the DB schema are untouched; deploy rebuilds only the sidecar, prod
orchestrator is not restarted (NFR-3).

Tests: tests/watchdog/test_proc_blocking_signal.py (TC-01..TC-06),
test_proc_collector.py (/proc parsing), test_tick_proc_blocking_integration.py
(TC-07), plus pid: host and proc-config assertions. Full pytest tests/ green (1930).

Refs: ORCH-111
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.env.example

@@ -569,6 +569,12 @@ ORCH_QG0_TITLE_MAX=200
 #   CONTAINERS     -> CSV of container names to watch (status != running/healthy).
 #   DOCKER_SOCK    -> path to the read-only docker.sock inside the container.
 #   DEPS           -> CSV of name=url dependency pings (empty -> no pings).
+#   PROC_ENABLED   -> ORCH-111 opt-in: alert on a long-lived test process (pytest)
+#                     orphaned on the host (needs `pid: host`, default OFF).
+#   PROC_AGE_MIN   -> minutes a test process may live before alerting; MUST exceed
+#                     max(merge_retest_timeout_s, coverage_run_timeout_s)/60.
+#   PROC_PATTERNS  -> CSV of cmdline substrings that mark the test-class (pytest).
+#   PROC_COOLDOWN_S-> per-signal re-alert throttle for proc_blocking.
 #   TG_BOT_TOKEN / TG_CHAT_ID -> the sidecar's OWN Telegram bot/chat (independent
 #                     of the orchestrator's; absent -> logs, does not send).
 WATCHDOG_ENABLED=true
@@ -588,5 +594,9 @@ WATCHDOG_QUEUE_DEPTH=20
 WATCHDOG_CONTAINERS=orchestrator
 WATCHDOG_DOCKER_SOCK=/var/run/docker.sock
 WATCHDOG_DEPS=
+WATCHDOG_PROC_ENABLED=false
+WATCHDOG_PROC_AGE_MIN=60
+WATCHDOG_PROC_PATTERNS=pytest
+WATCHDOG_PROC_COOLDOWN_S=1800
 WATCHDOG_TG_BOT_TOKEN=
 WATCHDOG_TG_CHAT_ID=