Shot-end handling: yield stabilization + tail trimming #325

Problem

When a shot stops, reaprime waits 4s to catch the final drips and update actualYield.
But this is invisible to the user, who usually lifts the cup the instant the shot
stops — corrupting actualYield. The post-stop "tail" also contains wrong
pressure/flow and is normally trimmed by the UI anyway.

Current state (implemented)

• trustedFinalYield: weight is latched at the machine-reported stop, then
  refined only by sensible post-stop increases (≤2 g/sample, ≤5 g total,
  flow <3 g/s). actualYield derives from this, not from scanning the raw trace.
  Cup removal / touch spikes no longer rewrite the yield.
• Trace stops at shot end (scale shots): the tail isn't recorded, so only the
  yield follows the drips — the graph doesn't.
• No-scale shots finish immediately: the settling window exists only to catch
  scale drips, so without a scale there's nothing to wait for.

Open questions / proposed changes

1. Drop the stored tail (scale shots)? Its only purpose was the final drips ->
   yield, which trustedFinalYield now captures independently. Remaining question
   is purely whether the wrong-pressure/flow, UI-trimmed tail rows are worth keeping.
2. Projection undershoot. SAW stops on projected weight, so the latch is
   under-target and must catch up post-stop. The current gating (flow ≤3 g/s,
   <2 g/sample) is tuned for drips, so a fast shot stopped with a large projection
   could undershoot. Proposal: anchor the allowed rise to the target (we stopped
   because projected ≥ target, so climbing to ~target shouldn't be flow-gated),
   apply strict drip/spike gating only beyond it.