fix: stroke arcs and splines analytically — opaque core, angle-independent weight

LICE_Arc never reaches opacity and ThickFLine's width is minor-axis. One
distance-to-polyline coverage mask, blended once, replaces both.

src/shell/instrument/CMakeLists.txt

@@ -64,6 +64,7 @@ if(WIN32 AND EXISTS "${VST3_SDK}/public.sdk/source/main/pluginfactory.cpp")
         editor_input_deck.cpp
         editor_input_browse.cpp
         editor_input_curve.cpp
+        editor_stroke.cpp
         editor_platform.cpp
         reasampler_embed.cpp
         reaper_bridge.cpp
@@ -87,7 +88,7 @@ if(WIN32 AND EXISTS "${VST3_SDK}/public.sdk/source/main/pluginfactory.cpp")
         waveform_view bank_sync browser_scroll param_slider tooltip
         theme component_geometry bank_grid trigger_seam envelope_overlay envelope_edit
         knob_deck deck_groups deck_values curve_popup spline_edit master_gain sample_usage
-        file_bytes curve_law)
+        file_bytes curve_law stroke_aa)
     # SDK_INC gives the REAPER VST3 interfaces + API header for the bridge; WDL_INC gives
     # LICE for the editor. The VST3 SDK headers arrive via vst3_sdk PUBLIC.
     target_include_directories(reasampler_vst PRIVATE ${REASAMPLER_SRC_DIR} ${SDK_INC} ${WDL_INC})