Reels: ease burst fade 0.08s → 0.12s

0.08s read as too abrupt; 0.12s keeps the burst clearly snappier than the
0.35s held-shot fade without jarring. Bumps RENDER_VERSION.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/reels/render.rs

@@ -39,7 +39,7 @@ const NARRATION_TAIL_SECONDS: f64 = 0.6;
 /// gentle dip; burst photos get a much snappier fade so the difference between
 /// a held shot and a quick burst is obvious.
 const SINGLE_FADE_SECONDS: f64 = 0.35;
-const BURST_FADE_SECONDS: f64 = 0.08;
+const BURST_FADE_SECONDS: f64 = 0.12;
 
 /// Video-clip framing. A clip plays at most this long, with its live audio
 /// ducked to `CLIP_DUCK_VOLUME` under the narration.
@@ -560,7 +560,7 @@ mod tests {
         assert!(g.contains("[v0][v1][v2]concat=n=3:v=1:a=0[v]"));
         assert!(g.contains("[3:a]apad[a]"));
         // Burst uses the much snappier fade (vs 0.35 for a held shot).
-        assert!(g.contains("d=0.08"));
+        assert!(g.contains("d=0.12"));
         assert!(!g.contains("d=0.35"));
     }