Output: Add render progress logging

README.md

@@ -166,6 +166,12 @@ cached/direct-fallback image counts.  Pass `--psf-direct` to use the slower
 whose required HDR-tail support exceeds the cache radius selects that reference
 path automatically.
 
+The PSF-cache completion line is printed before tracing and catalog splatting
+begin.  For long renders, pass `--verbose` to print catalog-prefetch state,
+splat and image-write boundaries without adding work to the splat hot path.
+Movie renders always print one summary per time slab; `--verbose` also prints
+the ray counts before each slab is loaded.
+
 For PSF validation only, `make psf-hdr-test` builds
 `build/minkowski_psf_hdr_test`, a separate binary with a `--hdr-output PATH`
 option.  It writes the pre-tone-mapping RGB framebuffer as a 32-bit float PFM