Adv 2.0 D&D Phase R7: post-completion audit hardening

High-priority fixes from the multi-agent audit of Adventure 2.0:

- Phase 11 nil-deref cluster: zoneOrFallback() helper replaces 8 unsafe
  getZone(_) sites in dnd_zone_cmd.go. Corrupted zone IDs render a
  placeholder instead of panicking.
- Briefing/recap idempotency: deliverBriefing/deliverRecap now claim
  the rollover via a conditional UPDATE. Double-fires from clock skew
  or restart become no-ops; supply burn and day++ no longer reapply.
- Graceful ticker shutdown: AdventurePlugin gains stopCh + Stop(); all
  11 background tickers now select on stopCh in addition to ticker.C.
- Mood decay (§3.2): math.Round(elapsed*2) replaces int() truncation
  so sub-hour gaps decay correctly.
- 24h auto-abandon (§4.3): getActiveZoneRun returns clean slate and
  abandons stale runs whose LastActionAt is over 24h old.
- Respec / auto-migrate orphan cleanup: !respec and the auto-migrated
  draft wipe now abandon active zone runs and expeditions before
  deleting the dnd_character row.
- Phase R combat-link: applyBossDefeatThreat now wired from
  resolveBossRoom (-20 threat); applyRoomCombatThreatForUser adds
  +5/+8 from non-boss/elite kills (§8.1).
- Starvation → forced extraction: briefing-time check forces extract
  with §10.2 coin tax when supplies hit zero.
- GMNat20/Nat1 narration wired into resolveCombatRoom and
  resolveBossRoom (nat-20 takes precedence over nat-1).
- Treasure-undo race: LoadAndDelete on both timer-fire and `undo`
  paths so only one side wins.
- Battle Master: Disarming, Menacing, Parry maneuvers added (3 → 6
  of 10). Remaining 4 (Pushing, Goading, Riposte, Commander's Strike)
  documented inline as needing ally/reaction mechanics the engine
  doesn't model.
- Threat-70 warning: tracked in RegionState["siege_warning_fired"]
  so a drop-and-recross doesn't re-fire the beat.
- region_state JSON decode error now logged via slog.Warn instead
  of silently discarded.

Failing TestProdDB_DnDLayer fixed via option (a): track migrated
characters and only run round-trip / idempotency assertions on those,
skipping pre-existing prod-DB rows accumulated from live bot use.

New tests in dnd_audit_phase_R7_test.go cover: 24h auto-abandon,
briefing double-fire idempotency, threat-70 warning idempotency,
multi-region extract→resume state preservation, and starvation
forced-extraction.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/dnd_zone.go

@@ -1,6 +1,9 @@
 package plugin
 
-import "sort"
+import (
+	"fmt"
+	"sort"
+)
 
 // Phase 11 D1a — zone registry. Implements `gogobee_dungeon_zones.md` §5.
 //
@@ -127,6 +130,25 @@ func getZone(id ZoneID) (ZoneDefinition, bool) {
 	return z, ok
 }
 
+// zoneOrFallback returns the registered ZoneDefinition or, if the id
+// is unknown (corrupted DB row, dropped registration), a safe
+// placeholder so display strings don't panic. Use this at non-fatal
+// callsites that just need a Display/Hook/Atmosphere to print.
+func zoneOrFallback(id ZoneID) ZoneDefinition {
+	if z, ok := dndZoneRegistry[id]; ok {
+		return z
+	}
+	return ZoneDefinition{
+		ID:         id,
+		Display:    fmt.Sprintf("(unknown zone %q)", string(id)),
+		Hook:       "",
+		Atmosphere: "",
+		Tier:       1,
+		LevelMin:   1,
+		LevelMax:   1,
+	}
+}
+
 // zonesForLevel returns all zones a player at dndLevel may enter.
 // Per design doc §2: a player cannot enter a zone more than 2 tiers
 // above their current level. We approximate "current tier" as