chore(lefthook): grandfather 3 pre-existing over-cap engine files

screenshotService.ts (516 LoC), frameCapture.ts (791 LoC), and
videoFrameInjector.ts (610 LoC) are pre-existing over the 500-line
lefthook cap added in #748. Any PR touching them currently must ship
with --no-verify (see PR #787 which hit exactly this).

This change extends the filesize hook's case-allowlist (already used
for useTimelinePlayer.ts + App.tsx) to cover the three engine files
so future PRs to them can land cleanly. Splitting them properly is a
separate effort tracked as tech debt; this unblocks the hf#677 perf
chain in the meantime.

Author: vanceingalls

lefthook.yml

@@ -17,7 +17,7 @@ pre-commit:
       exclude: "(\\.test\\.(ts|tsx)$|\\.generated\\.)"
       run: |
         for f in {staged_files}; do
-          case "$f" in *useTimelinePlayer.ts|*App.tsx) continue ;; esac
+          case "$f" in *useTimelinePlayer.ts|*App.tsx|*screenshotService.ts|*frameCapture.ts|*videoFrameInjector.ts) continue ;; esac
           lines=$(wc -l < "$f")
           if [ "$lines" -gt 500 ]; then
             echo "ERROR: $f has $lines lines (max 500)"