wip(L5, side branch): Linux offscreen captures + sampled far-LOD gate + no-op octave cutoff

Not for assembler/world: no octave qualifies under the cutoff's supremum criterion (world
unchanged), and the build is +4.6% slower than L4 with the flag off (reviewer interleaved W12).
Keeps the working EGL/GLES capture path and a gate whose metric is vertical height error, which
overstates screen error on steep slopes; its "exact far meshes exceed 1 px / 126 px pop" claims are
unconfirmed. See Linux5/REPORT.md "Orchestrator review".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ED33VnqepD4YY6gDAAA832

Standalone/BuildLinux.sh

@@ -33,6 +33,8 @@ if [[ "$FP_CONTRACT" != "default" && "$FP_CONTRACT" != "off" && "$FP_CONTRACT" !
 fi
 command -v "$COMPILER" >/dev/null || { printf 'Compiler not found: %s\n' "$COMPILER" >&2; exit 2; }
 command -v ar >/dev/null || { printf 'ar not found\n' >&2; exit 2; }
+command -v pkg-config >/dev/null || { printf 'pkg-config not found\n' >&2; exit 2; }
+pkg-config --exists egl glesv2 libpng || { printf 'EGL, GLESv2, and libpng development files are required\n' >&2; exit 2; }
 
 BUILD_DIR="$ROOT/Build/linux-$VARIANT"
 BIN_DIR="$ROOT/bin/linux"
@@ -117,5 +119,10 @@ CORE_LIBRARY="$BUILD_DIR/libVoxelForgeCore.a"
 "$(command -v ar)" rcs "$CORE_LIBRARY" "${CORE_OBJECTS[@]}"
 OUTPUT="$BIN_DIR/VoxelForgeCoreHeadless-$VARIANT"
 "$COMPILER" -pthread "${LEGACY_OBJECTS[@]}" "$CORE_LIBRARY" -o "$OUTPUT"
+CAPTURE_OUTPUT="$BIN_DIR/VoxelForgeOffscreenCapture-$VARIANT"
+"$COMPILER" -std=c++20 -O2 -fno-fast-math -pthread \
+    "$ROOT/Source/LinuxOffscreenCapture.cpp" -o "$CAPTURE_OUTPUT" \
+    $(pkg-config --cflags --libs egl glesv2 libpng)
 printf 'Built Core library: %s\nBuilt headless benchmark: %s\n' "$CORE_LIBRARY" "$OUTPUT"
+printf 'Built EGL offscreen capture: %s\n' "$CAPTURE_OUTPUT"
 printf 'Compiler: %s | variant: %s | fp-contract: %s | jobs: %s\n' "$COMPILER" "$VARIANT" "$FP_CONTRACT" "$JOBS"