Adv 2.0 D&D Phase 12 E2c: Siege Mode effects + threat-70 warning

§8.3 siege economics:
- applyDailyBurn now takes an explicit siege flag and enforces a 2× floor
  on supply burn even when HarshMod is below 2 (tier-1 zones still get
  starved out per spec).
- currentBurn mirrors the same precedence so status/briefing readouts
  stay consistent.
- Briefing rollover passes e.SiegeMode through, decoupling siege from
  the harsh-conditions composite.

§8.3 threat-70 warning: applyDailyThreatDrift emits a one-time
appendApproachingSiegeLog when the level crosses 70 (prevLevel<70 and
new level≥70). Pulls from a new flavor.ThreatClockApproachingSiege pool
seeded with the spec's verbatim warning beat plus two voice-matched
alternates.

Other siege effects (boss +20 HP / Legendary Resistance, cleared-room
respawn, no-short-rest enforcement) stay deferred to the combat-link
phase — ThreatBandInfo already exposes the flags that engine will read.

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

internal/plugin/dnd_expedition_cycle.go

@@ -151,8 +151,8 @@ func scanExpeditionRows(rows *sql.Rows) ([]*Expedition, error) {
 // morning briefing DM, appends a log entry, and stamps last_briefing_at.
 func (p *AdventurePlugin) deliverBriefing(e *Expedition, now time.Time) error {
 	// Advance day + supply burn happen together at the morning rollover.
-	harsh := e.ThreatLevel > 60 || e.SiegeMode || e.TemporalStack > 0
-	newSupplies, burn := applyDailyBurn(e.Supplies, harsh)
+	harsh := e.ThreatLevel > 60 || e.TemporalStack > 0
+	newSupplies, burn := applyDailyBurn(e.Supplies, harsh, e.SiegeMode)
 	if err := updateSupplies(e.ID, newSupplies); err != nil {
 		return err
 	}