Merge origin/new-newnassets: new LPC rat assets and animations

Cherry-picked from new-newnassets (3 commits):
- bdf5a8d Add new start animation asset for game launch
- 5f2d09f Fix rat animations and restore map tiles
- 2e2c5bb feat: add LPC-style rat assets, sprite generation scripts, and grid extraction tools

Conflicts resolved:
- engine/sdl2.py: kept 'if scale:' wrapper (compatible, default scale=True)
- units/rat.py: kept animation frame computation (partial_move * 4)
- 12 PNG files (BMP_BABY/MALE/FEMALE_*): kept new-newnassets versions

Cleanup applied: removed ~480 working artifacts not appropriate for the
production repo:
- 25 PNG in repo root (male_rats*.png, spritesheet*.png)
- 416 tile extracts in tools/lpc_extract/grid/
- scattered debug PNGs (bushes, preview, montages, etc.)
- early iteration scripts (animate_rat v1-v4, restyle v2-v10, etc.)

Kept: 32 new LPC-style sprites in assets/Rat_LPC_Style/, 4 animation
sprite sheets in assets/Rat_Animated/, 64 updated Rat sprites, 22
final-version generator scripts, plus all .py/.md updates.

tools/lpc_extract/sample_bush.py

@@ -0,0 +1,14 @@
+from PIL import Image
+
+img = Image.open('/home/enne2/dev/mice/tools/lpc_extract/bushes.png').convert('RGBA')
+pixels = img.load()
+
+print("Top edge transition:")
+for y in range(0, 48):
+    if pixels[48, y][3] > 0:
+        print(f"y={y}: {pixels[48, y]}")
+
+print("\nBottom edge transition:")
+for y in range(95, 48, -1):
+    if pixels[48, y][3] > 0:
+        print(f"y={y}: {pixels[48, y]}")