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_cycle.go

@@ -157,7 +157,7 @@ func (p *AdventurePlugin) deliverBriefing(e *Expedition, now time.Time) error {
 	forceDouble := applyZoneTemporalPreBurn(e, e.CurrentDay+1)
 
 	// Advance day + supply burn happen together at the morning rollover.
-	harsh := e.ThreatLevel > 60 || e.TemporalStack > 0
+	harsh := e.ThreatLevel > 60 || zoneTemporalHarsh(e)
 	newSupplies, burn := applyDailyBurn(e.Supplies, harsh, e.SiegeMode || forceDouble)
 	if err := updateSupplies(e.ID, newSupplies); err != nil {
 		return err