Decode the IGC coefficient value encoding: bit-serial x2 place values

The payload floats group into clean x2 doubling chains (0.0079 0.016 0.032 ...
1.009) = a coefficient stored as its binary place values C*2^k across the
bit-planes, exactly how a bit-serial adder holds a number. Recovered base
coefficients correlate with the object's own screen-space edge/z slopes
(decode_corr.py, chain_decode.py), so igc_array.py's inputs are cross-validated
against the compiled stream. Fixed-point scales from FOOTER.SS (Czscale=2^20,
Ctexscale=2^16). Readout §02 + decode notes updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

emulator/firmware-decomp/render-readout.html

@@ -262,6 +262,14 @@
 +01c  <span class="ad">00000022</span>   <span class="cm">; bit-plane 0x22 …</span></pre>
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+    <p class="sub" style="margin-top:14px">Pull the floats out of those payloads and they
+    line up into clean <b>×2 chains</b> —
+    <span class="mono">0.0079 · 0.016 · 0.032 · 0.063 · 0.126 · 0.252 · 0.504 · 1.009</span> —
+    a coefficient stored as its binary place values <span class="mono">C·2ᵏ</span>, one per
+    bit-plane, exactly how a bit-serial adder holds a number. The recovered bases match the
+    object's own edge and z slopes computed from the captured vertices — so the coefficients
+    feeding the array simulator (§05) are <b>cross-validated against the compiled stream the
+    hardware actually shipped</b>.</p>
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