Add composable ASCII art with per-cell effects and explicit effect loading

Implements ascii_fx_zone effect that allows applying arbitrary sexp effects
to each character cell via cell_effect lambdas. Each cell is rendered as a
small image that effects can operate on.

Key changes:
- New ascii_fx_zone effect with cell_effect parameter for per-cell transforms
- Zone context (row, col, lum, sat, hue, etc.) available in cell_effect lambdas
- Effects are now loaded explicitly from recipe declarations, not auto-loaded
- Added effects_registry to plan for explicit effect dependency tracking
- Updated effect definition syntax across all sexp effects
- New run_staged.py for executing staged recipes
- Example recipes demonstrating alternating rotation and blur/rgb_split patterns

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

sexp_effects/test_interpreter.py

@@ -150,6 +150,68 @@ def test_effect_execution():
     return passed, failed
 
 
+def test_ascii_fx_zone():
+    """Test ascii_fx_zone effect with zone expressions."""
+    print("Testing ascii_fx_zone...")
+
+    interp = get_interpreter()
+
+    # Load the effect
+    effects_dir = Path(__file__).parent / "effects"
+    load_effects_dir(str(effects_dir))
+
+    # Create gradient test frame
+    frame = np.zeros((120, 160, 3), dtype=np.uint8)
+    for x in range(160):
+        frame[:, x] = int(x / 160 * 255)
+    frame = np.stack([frame[:,:,0]]*3, axis=2)
+
+    # Test 1: Basic without expressions
+    result, _ = run_effect('ascii_fx_zone', frame, {'cols': 20}, {})
+    assert result.shape == frame.shape
+    print("    Basic run: OK")
+
+    # Test 2: With zone-lum expression
+    expr = parse('(* zone-lum 180)')
+    result, _ = run_effect('ascii_fx_zone', frame, {
+        'cols': 20,
+        'char_hue': expr
+    }, {})
+    assert result.shape == frame.shape
+    print("    Zone-lum expression: OK")
+
+    # Test 3: With multiple expressions
+    scale_expr = parse('(+ 0.5 (* zone-lum 0.5))')
+    rot_expr = parse('(* zone-row-norm 30)')
+    result, _ = run_effect('ascii_fx_zone', frame, {
+        'cols': 20,
+        'char_scale': scale_expr,
+        'char_rotation': rot_expr
+    }, {})
+    assert result.shape == frame.shape
+    print("    Multiple expressions: OK")
+
+    # Test 4: With numeric literals
+    result, _ = run_effect('ascii_fx_zone', frame, {
+        'cols': 20,
+        'char_hue': 90,
+        'char_scale': 1.2
+    }, {})
+    assert result.shape == frame.shape
+    print("    Numeric literals: OK")
+
+    # Test 5: Zone position expressions
+    col_expr = parse('(* zone-col-norm 360)')
+    result, _ = run_effect('ascii_fx_zone', frame, {
+        'cols': 20,
+        'char_hue': col_expr
+    }, {})
+    assert result.shape == frame.shape
+    print("    Zone position expression: OK")
+
+    print("  ascii_fx_zone OK")
+
+
 def main():
     print("=" * 60)
     print("S-Expression Effect Interpreter Tests")
@@ -159,6 +221,7 @@ def main():
     test_interpreter_basics()
     test_primitives()
     test_effect_loading()
+    test_ascii_fx_zone()
     passed, failed = test_effect_execution()
 
     print("=" * 60)