Step down when losing ground, not when slower than a constant

Build 117.

A campus M4 Pro sat in the red with nobody listening and no language being
translated — so transcription alone. Measured over SSH: sentences 4.2-4.7 s
against roughly 4-5 s of audio, queue 46 deep, lag 152 s and still climbing.

The mechanism built to catch exactly this could not fire. It triggers past 8 s,
on the reasoning that 8 s means slower than people talk. That held when a chunk
could be 8 s long; chunks are capped at HARD_CUT_MAX, 5.5 s. A 4.4 s sentence is
already losing and never comes near 8 s, so the ladder never stepped down and
the backlog grew without bound.

It now compares against the audio the chunk actually held. Two details are
measured rather than chosen: the margin is 0.85, because the Mini's 4.4 s
against 4.5 s was NOMINALLY faster than real time while still losing — the work
outside that timer (segmenting, the preview model sharing the GPU, the
scheduler) loses on its own. And it requires a backlog of five, so one slow
sentence on a healthy machine touches nothing. Checked against eight cases
including the Mini's real numbers and a healthy M2 Max.

The old absolute rule stays for a model that is genuinely hung.

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

app/package.json

@@ -2,7 +2,7 @@
   "name": "church-translate-engine",
   "productName": "Church Translate",
   "version": "3.23.2",
-  "buildNumber": 116,
+  "buildNumber": 117,
   "private": true,
   "description": "Live sermon translation — self-contained: captures audio, transcribes, translates, and serves the congregation page itself",
   "main": "main.js",
@@ -106,7 +106,7 @@
       ]
     },
     "asar": false,
-    "buildVersion": "116",
+    "buildVersion": "117",
     "win": {
       "target": [
         {