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>

docs/usage.md

@@ -479,6 +479,48 @@ that takes longer than `timeout` — each is a warning, and the affected text go
 to the TTS with its digits intact. The worker is started once per run and exits
 before TTS generation begins, so it is not holding VRAM while Higgs works.
 
+## The output pane
+
+It follows the newest output only while you are already at the bottom. Scroll
+up and it stays where you put it, however much arrives in the meantime; scroll
+back down and it resumes following. There is nothing to click either way.
+
+That matters during a run, where output lands several times a second and ffmpeg
+redraws its progress bar continuously — scrolling back to read an earlier
+warning was impossible while every frame yanked the view to the end.
+
+## The queue log
+
+Every GUI run writes `queue.log` into the **first queued video's job folder** —
+which for a single-video run is simply its own. It records what went wrong, not
+what happened: the output pane already carries every clip and placement, and
+none of that helps at 8 a.m. when you want to know why a queue stopped.
+
+```
+===== queue started 2026-08-13 09:09:17 — 2 job(s) =====
+09:09:17  --- generate: good.mkv
+09:09:17  ComfyUI unreachable (<urlopen error [Errno 111] Connection refused>) [1/3 for this clip].
+09:09:48      finished OK
+09:09:48  --- generate: bad.mkv
+09:10:04  ffmpeg error (Mixing lektor audio track):
+09:10:04  /dev/null: Invalid data found when processing input
+09:10:04      FAILED with exit code 1 — 0 job(s) cancelled
+09:10:04      last 15 line(s) before it stopped:
+09:10:04        | …
+```
+
+Each job is bracketed by a start line and its outcome. In between go the lines
+that report a problem — warnings, tracebacks, ffmpeg errors, guard rejections,
+clips that crashed the backend or came back cut off mid-word.
+
+**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, so an exit code would otherwise be recorded with no
+explanation.
+
+The file is appended to, never truncated, so it is a record across runs and a
+crash cannot cost you the previous session.
+
 ## The backend's lifecycle
 
 ComfyUI is normally started once and left running. The script manages it when it
@@ -496,6 +538,13 @@ has to:
 Its output goes to `comfyui.log` next to the script as well as to the terminal
 window, so a crash can be diagnosed after the fact.
 
+That file is **capped at 120,000 lines** (roughly 10 MB). Past that the oldest
+lines are dropped, on backend start and every five minutes while the GUI is
+open. It is trimmed in place rather than rotated: there is one file to look at
+after a crash, no `.1`/`.2` to hunt through, and rewriting in place is also what
+keeps `tee` writing to it — replacing the file would leave the backend appending
+to an unlinked inode and every later line would vanish.
+
 The GUI has a **ComfyUI** button showing the same state: `Start ComfyUI` when it
 is down, `ComfyUI ●` when it is answering, `ComfyUI ◍` when it holds the port but
 does not answer. Pressing it starts or restarts.