P4: transcribe exact FUN_180529fe0 mask chain (structural, not yet calibrated)

framed_model.cpp now follows the decoded mono-path structure:
  level -> scale(0x540870*0x54088c/0x1a0) -> IIR1 leaky(A1/B1) -> IIR2(A2/B2)
  -> exp2(0.5*(mask-blend)) -> combine/acc -> warp -> IIR3(A3/B3)x2 -> dry/wet
IIR stages are the real live tables (iir_leaky y=A*acc+B*x, B=1-A). Removed the
empirical mask_lut=(1/(1+K*acc))^n. Not numerically calibrated yet: exp2 bigkernel
exact semantics + PRNG prologue (fVar30) + FFT-conv still TBD; t1kq depth -2.9 vs
-14.98 dB ref.

dsp/CMakeLists.txt

@@ -23,6 +23,7 @@ add_library(soothe2_dsp SHARED
     leveltrack.cpp
     framed_model.cpp
     rt_weights.cpp
+    rt_mask_tables.cpp
 )
 
 add_executable(soothe2_harness harness.cpp)