§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>