feat(qg0): configurable QG-0 title limit via ORCH_QG0_TITLE_MAX (default 200)

Replace the hardcoded `len(name) > 80` cap in the QG-0 entry validation
(_qg0_errors) with a configurable Settings.qg0_title_max (env
ORCH_QG0_TITLE_MAX, default 200). The 80-char cap was a hygiene limit, not
structural, so valid 81-200 char titles were rejected without a business
reason. The limit is read dynamically per call and the error text interpolates
the active value.

Graceful degradation (AC-3, self-hosting safety): an empty/non-numeric env
value no longer crashes the process on startup. A field_validator(mode="before")
intercepts the raw env before int-parsing and falls back to 200 (never raises),
suppressing pydantic ValidationError.

Additive and backward-compatible (default 200 > old 80). Invariants unchanged:
STAGE_TRANSITIONS, QG_CHECKS registry, DB schema, slug [:30], lower limits,
soft-QG-0 warning path, API.

Refs: ORCH-069

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.env.example

@@ -199,3 +199,10 @@ ORCH_POST_DEPLOY_FAIL_THRESHOLD=3
 ORCH_POST_DEPLOY_5XX_THRESHOLD=0.5
 ORCH_POST_DEPLOY_AUTO_ROLLBACK=false
 ORCH_POST_DEPLOY_BASE_URL=http://localhost:8500
+
+# ── QG-0 entry validation (ORCH-069) ──────────────────────────────────────────
+# Upper title-length limit for the QG-0 entry gate (_qg0_errors). The old 80-char
+# cap was a hygiene limit, not structural (slug is cut to [:30] independently, the
+# DB title TEXT is unbounded). Default 200. An invalid/empty value gracefully
+# degrades to 200 (the process never crashes on startup).
+ORCH_QG0_TITLE_MAX=200