Long expeditions D1-d: T4 zones to new 28-34 room band

Both T4 zones follow the D1-a/b/c pattern: extend the graph so the
longest entry→boss walk lands in band, keep the zone's authored
topology intact.

  underdark         (T4): 10 → 46 nodes, longest 30 (band 28-34)
  feywild_crossing  (T4):  9 → 53 nodes, longest 30 (band 28-34)

Topology preserved per zone:
- Underdark: 4-region authoring intact (every node carries a valid
  RegionID); 3-way fork1 (drow R2 / illithid R3 / deep_chasm R1)
  with LockNone / LockPerception / LockStatCheck CON; deep_chasm
  intentionally stays R1; all three arms converge at the R4
  throne_approach merge. Adds the missing Trap anchor (Collapsed
  Arch) in the R1 preamble.
- Feywild Crossing: woven forks intact — hag_circle still has two
  incoming edges (one per first-stage path), time_eddy stays
  grove-exclusive, illusion_garden stays marsh-exclusive, fork1
  remains CHA-vs-Perception with no LockNone option. Adds the
  missing Trap anchor (Cursed Thicket) and a fae_court MERGE so
  the three second-stage endings converge into one final boss
  approach instead of triplicating it.

MinRooms/MaxRooms re-pitched 8-10 → 28-34 so the dice fallback also
lands in band for any future graphless variant.

T5 zones (dragons_lair, abyss_portal) deferred to D1-e — those
need a RegionID backfill on top of the length extension since their
regionsByZone entries are not currently honored by their graphs.

internal/plugin/dnd_zone.go

@@ -548,8 +548,8 @@ func zoneUnderdark() ZoneDefinition {
 		Faction:    "Drow, Mind Flayers, Beholders (far), Ropers, Hook Horrors",
 		Atmosphere: "Absolute darkness, phosphorescent mushroom groves, vast underground seas, carved drow cities in the distance, things older than the surface world.",
 		Hook:       "There is a world below the world. It has its own cities, its own wars, its own sky — which is stone, and has never once been kind. I speak more quietly here. Something might be listening.",
-		MinRooms:   8,
-		MaxRooms:   10,
+		MinRooms:   28,
+		MaxRooms:   34,
 		Enemies: []ZoneEnemy{
 			// Phase 5-C: underdark ran 88% (band 45-65, way over)
 			// at the T4 centerline — its sibling feywild sat at
@@ -605,8 +605,8 @@ func zoneFeywildCrossing() ZoneDefinition {
 		Faction:    "Hags, Redcaps, Will-o-Wisps, Fomorians, Unseelie Fey",
 		Atmosphere: "Impossible beauty, treacherous whimsy, time distortion, rules that change without notice, bargains with terrible fine print.",
 		Hook:       "The veil between worlds is thin here. Colors are too saturated. The mushrooms are too large. A small creature made of starlight just offered you a deal. I advise extreme caution regarding deals.",
-		MinRooms:   8,
-		MaxRooms:   10,
+		MinRooms:   28,
+		MaxRooms:   34,
 		Enemies: []ZoneEnemy{
 			// Phase 5-C: feywild trailed at 54% (band 45-65, but
 			// the design goal was to close the 30pp gap with its