Adv 2.0 D&D Phase 12 E3c: Underforge heat accumulation

§7.3 heat stacks: +1/day in the Underforge (cap 10), persisted via
new updateTemporalStack helper. Band thresholds:
  • 1–3 ambient (no narration)
  • 4–6 warning band (combat fire damage applies, narration logged)
  • 7–9 supply band (forces harsh-conditions burn = +50%, narration)
  • 10 critical (exhaustion narration, log entry)

Fortified/base camp long rest in the Underforge drops heat by 2
(updates briefing's "Fortified rest" summary line), per §7.3.

Replaces the placeholder `TemporalStack > 0 → harsh` predicate in
deliverBriefing with zoneTemporalHarsh(), which is now per-zone aware
— Heat 1–3 in the Underforge is correctly flavor-only and no longer
prematurely doubles supply burn from Day 1.

Combat-side knobs (+1d4 fire round-start damage at heat 4–6, dis CON
saves at 7–9, -2 to all rolls at 10) are exposed via heat band but
not yet applied — combat-link phase reads heat band off the active
expedition.

Reuses flavor.UnderforgHeapWarning / UnderforgHeapCritical per
feedback_reuse_existing_flavor.

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

internal/plugin/dnd_expedition.go

@@ -364,6 +364,16 @@ func applyThreatDelta(expID string, delta int, reason string) error {
 	return err
 }
 
+// updateTemporalStack persists the zone-temporal stack (heat / instability).
+func updateTemporalStack(expID string, stack int) error {
+	_, err := db.Get().Exec(`
+		UPDATE dnd_expedition
+		   SET temporal_stack = ?,
+		       last_activity = CURRENT_TIMESTAMP
+		 WHERE expedition_id = ?`, stack, expID)
+	return err
+}
+
 // advanceExpeditionDay bumps current_day by one. Real-time day cycle (E1d)
 // calls this from the 06:00 cron.
 func advanceExpeditionDay(expID string) error {