Added Airy and PSF via FFT. Decided to make it a C2 feature

readme.md

@@ -170,10 +170,12 @@ cargo run --release -p resolved-showcase -- --serve 0.0.0.0:8010
   3 times and rolls highlights off to white at saturation. `--out` is the same
   either way.
 - `--timings N` renders N frames and reports setup and per-frame times.
-- `--lighting L0|L1` and `--camera C0|C1` pick the fidelity tiers (default
+- `--lighting L0|L1` and `--camera C0|C1|C2` pick the fidelity tiers (default
   L0 and C0). `--supersampling N` renders each pixel as N x N finer ones from C1
-  (default 2). A tier the scene or the data cannot support stops with an error
-  naming what is missing.
+  (default 2). `--psf-reach N` sets how far in pixels camera C2's PSF must reach
+  (default 16; it reaches as far as its FFT grid allows, 64 px at 1920 x 1080 and
+  2 x 2). A tier the scene or the data cannot support stops with an error naming
+  what is missing.
 - `--seed N` and `--frame N` pick the detector noise at camera C1 (default 0
   and 0): the same seed and frame give the same image.
 - `--data DIR` says where the tiers' data is (`earth/bmng-2004-MM.jpg`,
@@ -208,9 +210,12 @@ lens blur (a Gaussian PSF) applied to the scene rendered 2 x 2 finer than the
 pixels, the Sun, Moon and Earth at their apparent positions (light time
 and aberration), detector noise (shot, dark current and read noise, seeded
 and reproducible), the detector's fixed pattern (PRNU, DSNU and hot pixels),
-and blooming along columns or into neighbors. Planned, in order:
+and blooming along columns or into neighbors. Camera C2 adds diffraction
+(the Airy pattern, averaged over each channel's band) and measured PSFs,
+applied with their wings by FFT. Planned, in order:
 
-- Camera: the C1 checkpoint, then diffraction and measured PSFs (C2).
+- Camera: the C1 and C2 checkpoint, their rows in the table above with
+  sample images.
 - Lighting: BRDF and spectral materials, atmospheric scattering, clouds, lunar
   terrain.
 - Portable ray tracing, path tracing, and label outputs for ML.