fix: update AGENTS.md and specs for incursion day, elemental matchups, golem count, and descent mechanics

AGENTS.md

@@ -114,7 +114,7 @@ ManaDrainPerTick = drainBase × (1 + (XP / difficultyFactor)^0.4)
 - Stacking cost: each additional stack costs 20% more
 
 ### Golemancy
-- 10 golems total: 1 base (Earth) + 3 elemental (Steel, Crystal, Sand) + 6 hybrid (Lava, Galvanic, Obsidian, Prism, Quicksilver, Voidstone)
+- 12 golems total: 1 base (Earth) + 3 elemental (Steel, Crystal, Sand) + 6 hybrid (Lava, Galvanic, Obsidian, Prism, Quicksilver, Voidstone) + 2 advanced
 - Golems slots: `floor(fabricatorLevel / 2)`, max 5 at level 10
 - Hybrid golems require Enchanter 5 + Fabricator 5
 
@@ -130,14 +130,17 @@ ManaDrainPerTick = drainBase × (1 + (XP / difficultyFactor)^0.4)
 ### Combat
 - Cast-speed based: `castProgress += HOURS_PER_TICK × spellCastSpeed × attackSpeedMult`
 - Elemental bonuses: super effective (1.5×), same element (1.25×), weak (0.75×), neutral (1.0×)
-- Element opposites: fire↔water, air↔earth, light↔dark, lightning→earth
+- Element opposites (bidirectional): fire↔water, air↔earth, light↔dark, frost↔fire
+- Element counters (directional): lightning→water (lightning counters water), earth→lightning (earth counters lightning)
+- Composite element counters: blackflame counters frost/water/light (and they counter blackflame); radiantflames counters frost/water/dark (and they counter radiantflames)
+- All mana types double as spell elements
 - Enemy modifiers (max 2 per enemy): Armored, Agile, Mage, Shield, Swarm
 - Room types: Combat (default), Guardian (every 10th), Swarm (15%), Speed (10%), Puzzle (20% on every 7th floor)
 - Floor HP: `100 + floor × 50 + floor^1.7` for non-guardian floors
 
 ### Time & Incursion
 - `TICK_MS`: 200ms, `HOURS_PER_TICK`: 0.04, `MAX_DAY`: 30
-- Incursion starts day 5 (not day 20)
+- Incursion starts day 20
 - Incursion strength: `min(0.95, (totalHours / maxHours) × 0.95)`
 
 ### Prestige (Insight)