Install the whole backend from one script; queue log; UI fixes

install_comfyui.sh becomes install_backend.sh and now builds everything the app
needs, not just the speech half:

- Step 7 runs normalizer/setup.sh --model, which fetches both models: the open
  inflection model first, so the install gets as far as it can before anything
  can ask for credentials, then the gated fine-tune.
- A missing Hugging Face account is no longer fatal. Accepting a licence is the
  one thing an installer cannot do, so the rest installs, the verification
  reports "fallback only (gated model missing)", and the summary prints the
  three commands that finish it.
- --skip-normalizer, disk requirement 35 -> 55 GB, removal instructions and the
  step list updated to match.

Queue logging — queue.log in the first queued video's job folder, which for a
single-video run is its own:

- Records what went wrong rather than what happened: warnings, tracebacks,
  ffmpeg errors, guard rejections, clips cut off mid-word or that crashed the
  backend, and the --regen line carrying their numbers.
- ComfyUI failures *and* restarts, so the log shows the recovery rather than
  reading as though the run simply stopped. GUI-initiated backend actions go in
  too; they never pass through a job's pipe.
- A failure also dumps the job's last 15 lines. Keyword matching alone is not
  enough — ffmpeg says "Invalid data found when processing input" and nothing
  that looks like an error.

UI:

- The output pane follows new output only while already at the bottom. Scroll up
  and it stays there; scroll back down and it resumes. Reading an earlier
  warning during a run was impossible while every ffmpeg progress frame yanked
  the view to the end.
- The ComfyUI button's status dot is drawn as its own canvas item, so it can be
  green (answering) or amber (holds the port, does not answer). A "." inside the
  label could only ever be the same grey as the words.

comfyui.log is capped at 120,000 lines, trimmed on backend start and every five
minutes. Rewritten in place, never replaced: tee holds it open in append mode,
so swapping the inode would leave the backend writing to an unlinked file.

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

readme.txt

@@ -9,7 +9,7 @@ FULL DOCUMENTATION: see docs/
   docs/architecture.md     how the pipeline works internally
   docs/troubleshooting.md  diagnosed failure modes and their fixes
 
-Installer: ./install_comfyui.sh   (see docs/installation.md)
+Installer: ./install_backend.sh   (see docs/installation.md)
 
 This file remains as a condensed quick reference.
 
@@ -144,6 +144,7 @@ output/
       tts_assembled.flac — all clips assembled with correct timing (lossless)
       embedded_sub.srt — extracted embedded subtitle (only with --embedded-subs)
       video_fragment.mkv — extracted video segment (only when --end is used)
+      queue.log        — errors and warnings from GUI runs (first video of a queue)
   {stem}_lektor.mkv    — final video with two audio tracks + all original subtitles:
                            Track 0 — Original (source audio, stream-copied as-is)
                            Track 1 — Polish lektor (TTS + original mixed,