feat(capture): offline auto/manual tail via pure TailMode mapping

Add TailMode{None,Auto,Manual} + derived -72dB TRIMEND + 8s cap in render_settings;
wire into OfflineRenderBackend with snapshot/restore of the tail settings; add
CAPTURE_ITEM_TAIL/CAPTURE_TRACK_TAIL variant actions (plain actions stay exact-bounds).

src/main.cpp

@@ -510,8 +510,8 @@ static void RunCapture(const reasampler::CaptureActionDef& def)
     req.startSeconds = src.startSeconds;    // exact bounds — no rounding
     req.endSeconds   = src.endSeconds;
     req.wetDry       = 1.0;                 // wet post the FX left enabled by the scope
-    req.renderTail   = false;               // exact bounds, no tail (default)
-    req.tailMs       = 0.0;
+    req.tailMode     = def.tailMode;        // None (exact bounds) or Auto ("…with tail" variant)
+    req.tailMs       = 0.0;                 // Manual-only; no Manual action yet (future config/UI)
     req.sampleRate   = 0;                   // follow project rate
     req.channelCount = 2;
     req.bitDepth     = reasampler::WavBitDepth::Float32;  // deterministic, no dither
@@ -590,7 +590,7 @@ static void RunCaptureRealtimeTrack()
     req.startSeconds = src.startSeconds;                        // exact bounds — no rounding
     req.endSeconds   = src.endSeconds;
     req.wetDry       = 1.0;                                     // fully wet (post-fader tap)
-    req.renderTail   = false;
+    req.tailMode     = reasampler::TailMode::None;              // realtime tail is T2; exact bounds here
     req.tailMs       = 0.0;
     req.sampleRate   = 0;                                       // follow project rate
     req.channelCount = 2;