Run 15: known-nodes exploration (addendum stage 1), per-town debug, O(n^2) fix

Exploration addendum stage 1: per-NPC known-nodes. NPCs gather only from
resources they've personally sensed (radius 22) or been told about;
founders seed with home ground, children inherit parents' maps, node
knowledge diffuses between neighbors like skills. Starving NPCs venture
outward and sense as they go - non-random needs-driven exploration, the
seed of first contact. Repopulation preserved (seeding + survival food
fallback): all towns fed, population stable 86-109 over 240 days.

Debug screen rebuilt: the ~68-row per-villager roster (overflowing at
four-town scale) replaced with a per-town summary - pop, fed%, knowledge,
debris, state breakdown, buildings, culture-colored, plus world
births/deaths. Scales to any population.

Performance: added phase timers and measured instead of guessing - npc.Tick
was 94% of cost, O(n^2) via TickResting calling RestingOccupancy (full
population scan) per building per resting NPC. Fixed with a once-per-tick
occupancy cache on Building. npc phase ~4x faster and now linear; full
240-day four-town run in 180s, faster than the pre-exploration baseline.
Profiling scaffolding removed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/Building.cs

@@ -94,6 +94,11 @@ public class Building
 
     /// <summary>How many can sleep here. Expansion adds beds — growth has a
     /// human meaning, not just a bigger square.</summary>
+    /// <summary>Sleepers here, recomputed once per tick by GameManager —
+    /// so resting NPCs read a cached count instead of each re-scanning the
+    /// whole population per building (that was the sim's O(n²) hot spot).</summary>
+    public int Occupancy;
+
     public int RestCapacity =>
         Kind == BuildingKind.Shelter && IsComplete && !IsRuined ? 3 + Modules : 0;