Add API verification test suite and documentation

tests/docs/:
- API_FINDINGS.md: Comprehensive migration guide from deprecated to modern API
- test_*.py: 9 executable tests verifying actual runtime behavior
- screenshots/: Visual verification of working examples

tests/conftest.py:
- Add 'docs' and 'demo' to pytest collection paths

Key findings documented:
- Entity uses grid_pos= not pos=
- Scene API: Scene() + activate() replaces createScene/setScene
- scene.children replaces sceneUI()
- scene.on_key replaces keypressScene()
- mcrfpy.current_scene (property) replaces currentScene() (function)
- Timer callback signature: (timer, runtime)
- Opacity animation does NOT work on Frame (documented bug)

🤖 Generated with Claude Code (https://claude.ai/code)

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

tests/docs/test_quickstart_entities.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+"""Test for quickstart.md 'Game Entity' example.
+
+Original (DEPRECATED - lines 133-168):
+    mcrfpy.createScene("game")
+    grid = mcrfpy.Grid(20, 15, texture, (10, 10), (640, 480))
+    ui = mcrfpy.sceneUI("game")
+    player = mcrfpy.Entity((10, 7), texture, 85)
+    mcrfpy.keypressScene(handle_keys)
+    mcrfpy.setScene("game")
+
+Modern equivalent below.
+"""
+import mcrfpy
+from mcrfpy import automation
+import sys
+
+# Create scene using modern API
+scene = mcrfpy.Scene("game")
+scene.activate()
+mcrfpy.step(0.01)
+
+# Load texture
+texture = mcrfpy.Texture("assets/kenney_tinydungeon.png", 16, 16)
+
+# Create grid using modern keyword API
+grid = mcrfpy.Grid(
+    grid_size=(20, 15),
+    texture=texture,
+    pos=(10, 10),
+    size=(640, 480)
+)
+scene.children.append(grid)
+
+# Add player entity
+player = mcrfpy.Entity(grid_pos=(10, 7), texture=texture, sprite_index=85)
+grid.entities.append(player)
+
+# Add NPC entity
+npc = mcrfpy.Entity(grid_pos=(5, 5), texture=texture, sprite_index=109)
+grid.entities.append(npc)
+
+# Add treasure chest
+treasure = mcrfpy.Entity(grid_pos=(15, 10), texture=texture, sprite_index=89)
+grid.entities.append(treasure)
+
+# Movement handler using modern API
+def handle_keys(key, state):
+    if state == "start":
+        x, y = player.pos[0], player.pos[1]
+        if key == "W":
+            player.pos = (x, y - 1)
+        elif key == "S":
+            player.pos = (x, y + 1)
+        elif key == "A":
+            player.pos = (x - 1, y)
+        elif key == "D":
+            player.pos = (x + 1, y)
+
+scene.on_key = handle_keys
+
+# Center grid on player
+grid.center = (10, 7)
+
+# Render and screenshot
+mcrfpy.step(0.1)
+automation.screenshot("/opt/goblincorps/repos/McRogueFace/tests/docs/screenshots/quickstart_entities.png")
+
+print("PASS - quickstart entities")
+sys.exit(0)