Multi-region zones now default CurrentRegion to the entry region at
startExpedition; that region is also written to regions_visited so
the visited/cleared distinction is meaningful from Day 1.
MarkRegionVisited / MarkRegionBossDefeated expose the combat-link
hook surface. MarkRegionBossDefeated also flips Expedition.BossDefeated
when the cleared region's IsZoneBoss is set, since the zone-boss kill
is the same event from §7's POV (suppresses temporal accumulation,
kills further awareness pulses, etc.). setCurrentRegion is the
companion writer used by E4c's travel command.
!expedition status now shows the region line ("🗺 Region: Drow
Outpost (2/4)") with a ✓ marker when the region boss is down.
Spec: gogobee_expedition_system.md §11. Tier 4–5 zones (Underdark,
Dragon's Lair, Abyss Portal) split into 4 regions each. ExpeditionRegion
struct + per-zone registry; CurrentRegion(e) defaults to Order==1 when
unset; RegionState helpers persist regions_cleared / regions_visited /
base_camps as []string lists. Single-region zones return nil.
Tests cover registry shape (4 per zone, last is IsZoneBoss), lookups,
default current region, and round-trip persistence through DB.
