Fix right flipper: mirror its geometry and sweep it per-substep

The right flipper's arm was computed with the same +cos(angle) direction
as the left one, so it pointed into the right wall, off the 480px canvas
- only the left paddle was ever visible/playable.

- add physics.flipper_tip() which mirrors the right flipper (and use it
  in both collision and rendering)
- derive the flipper's surface velocity from actual tip displacement
  (scaled by contact radius), instead of a hand-signed angular formula
- advance flipper angles inside the collision substeps (6/frame while
  pressed) so a fast sweep can't jump past a resting ball; resting balls
  now get a real 'scoop' from either paddle
- verify: pixel probe shows both paddles on screen (L=1007, R=999 blue
  px); physics probe confirms each paddle launches a resting ball

game.py

@@ -9,7 +9,7 @@ import pygame
 from physics import (CV_W, CV_H, PLAY_L, PLAY_R, PLAY_T, PLAY_B, BALL_R,
                      CENTER_HOLE, OUTLANE_L, OUTLANE_R, DRAIN_Y, LAUNCH_DIR,
                      LAUNCH_MIN, LAUNCH_MAX, Table, FLIP_PIVOT_L, FLIP_PIVOT_R,
-                     FLIP_RADIUS, FLIP_LEN)
+                     FLIP_RADIUS, FLIP_LEN, flipper_tip)
 import font as pix
 
 # ---------------------------------------------------------------------------
@@ -195,9 +195,7 @@ def draw_sling(surf, s):
 
 def draw_flipper(surf, f, side):
     px, py = f["pivot"]
-    a = f["angle"]
-    tipx = px + math.cos(a) * f["length"]
-    tipy = py + math.sin(a) * f["length"]
+    tipx, tipy = flipper_tip(f)
     p0 = (int(px), int(py))
     p1 = (int(tipx), int(tipy))
     # shadow
@@ -210,7 +208,9 @@ def draw_flipper(surf, f, side):
         pygame.draw.circle(surf, C["flipper_d"], (ex, ey), 6)
         pygame.draw.circle(surf, C["flipper"], (ex, ey), 4)
     # cute stripe near the top edge
-    nx, ny = -math.sin(a), math.cos(a)
+    a = f["angle"]
+    side_sign = -1.0 if side == "R" else 1.0
+    nx, ny = -math.sin(a) * side_sign, math.cos(a)
     hx, hy = int(px + nx * 3), int(py + ny * 3)
     tx, ty = int(tipx + nx * 3), int(tipy + ny * 3)
     pygame.draw.line(surf, C["flipper_l"], (hx, hy), (tx, ty), 2)