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/effects/crt.sexp

@@ -1,10 +1,11 @@
 ;; CRT effect - old monitor simulation
-;; @param line_spacing int [1, 10] default 2
-;; @param line_opacity float [0, 1] default 0.3
-;; @param vignette float [0, 1] default 0.2
 
 (define-effect crt
-  ((line_spacing 2) (line_opacity 0.3) (vignette_amount 0.2))
+  :params (
+    (line_spacing :type int :default 2 :range [1 10])
+    (line_opacity :type float :default 0.3 :range [0 1])
+    (vignette_amount :type float :default 0.2)
+  )
   (let* ((w (width frame))
          (h (height frame))
          (cx (/ w 2))