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_cmd.go

@@ -257,8 +257,17 @@ func (p *AdventurePlugin) expeditionCmdStatus(ctx MessageContext) error {
 
 func currentBurn(exp *Expedition) float32 {
 	burn := exp.Supplies.DailyBurn
-	if exp.ThreatLevel > 60 || exp.SiegeMode {
-		// Harsh conditions: §4.1 / §8.3.
+	if exp.SiegeMode {
+		// §8.3: siege doubles supply burn outright, overriding HarshMod
+		// (which can be < 2 at low tiers).
+		mult := exp.Supplies.HarshMod
+		if mult < 2 {
+			mult = 2
+		}
+		return burn * mult
+	}
+	if exp.ThreatLevel > 60 {
+		// Harsh conditions: §4.1.
 		mult := exp.Supplies.HarshMod
 		if mult <= 0 {
 			mult = 1