per-floor extras + Ascension overrides + layer toggles

- atlasloot_extras: fit one transform per (kg_dungeon, floor_id) instead of mixing all kg bosses into one fit. Each AL extra is assigned to whichever floor's anchors it's nearest to (in AL coord space). Strat's Stonespine now correctly lands on floor 235 (Undead) instead of being hidden because the mixed-floor fit pushed it off.
- new data/ascension_overrides.json: per-name position/floor patches for places where Ascension diverges from retail. Seeded with Magistrate Barthilas → moved to the southern courtyard (3498, 3300 on Undead Side) per Ascension spawns.
- frontend renders extras only on their assigned floor; previously hard-coded to floor 0.
- new layer-toggle checkboxes (Enemies / Packs / Patrols / Icons) in the toolbar — flip patrols off if mob routes are noise for your route.

data/ascension_overrides.json

@@ -0,0 +1,12 @@
+{
+  "_comment": "Ascension-specific corrections to the upstream kg / AtlasLoot data. Each entry overrides where an enemy/extra is rendered. Match by tile_key + name (case-insensitive substring). pos is in kg pixel space (z=4 stitched image, 6144x4096). kg_floor_id picks the floor (omit if the dungeon is single-floor).",
+  "overrides": [
+    {
+      "tile_key": "stratholme",
+      "name": "Magistrate Barthilas",
+      "kg_floor_id": 235,
+      "pos": [3498, 3300],
+      "note": "Ascension moved Barthilas to the southern courtyard of the Undead Side"
+    }
+  ]
+}