style: apply ruff format across backend + scripts (line-length 100)

Mechanical, whole-tree `ruff format` pass — no behaviour change. Recorded in
.git-blame-ignore-revs (next commit) so git blame skips it.

backend/tests/test_run_ffmpeg.py

@@ -4,6 +4,7 @@ No ffmpeg here: a fake Popen stands in, so the reader threads, the 1s poll loop,
 and the bounded exit wait are all exercised on any machine. These are regression tests for a real
 deadlock: stderr was opened and never read, so a chatty ffmpeg filled the ~64KB pipe, blocked on its
 next write and never exited, and `proc.wait()` never returned."""
+
 import subprocess
 import time
 
@@ -109,7 +110,9 @@ def test_a_nonzero_exit_raises_with_the_stderr_tail(fake_popen):
         _FakeProc(_FakeStream([]), _FakeStream(["Invalid data found\n"]), returncode=2)
     )
     with pytest.raises(RuntimeError, match="Invalid data found"):
-        edit.run_ffmpeg(["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: False)
+        edit.run_ffmpeg(
+            ["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: False
+        )
     assert not proc.terminated  # it exited on its own; nothing to kill
 
 
@@ -119,7 +122,9 @@ def test_cancel_is_honoured_while_the_process_is_silent(fake_popen):
     proc = fake_popen(_FakeProc(_FakeStream(block=True), _FakeStream(block=True)))
     started = time.monotonic()
     with pytest.raises(edit.EditAborted):
-        edit.run_ffmpeg(["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: True)
+        edit.run_ffmpeg(
+            ["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: True
+        )
     assert proc.terminated
     assert time.monotonic() - started < 5  # not "whenever ffmpeg next speaks"
 
@@ -153,11 +158,11 @@ def test_a_callback_exception_still_stops_the_process(fake_popen):
 def test_a_process_that_ignores_sigterm_is_killed(fake_popen):
     # `_stop`'s escalation: terminate, wait 5s, then SIGKILL. Without it a cancel could park the
     # worker thread on a process that simply refuses to go.
-    proc = fake_popen(
-        _FakeProc(_FakeStream(block=True), _FakeStream(block=True), wait_timeouts=1)
-    )
+    proc = fake_popen(_FakeProc(_FakeStream(block=True), _FakeStream(block=True), wait_timeouts=1))
     with pytest.raises(edit.EditAborted):
-        edit.run_ffmpeg(["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: True)
+        edit.run_ffmpeg(
+            ["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: True
+        )
     assert proc.terminated and proc.killed
 
 
@@ -166,7 +171,9 @@ def test_a_process_lingering_after_eof_is_stopped_and_reported(fake_popen):
     # the worker thread on `proc.wait()` forever (the old code waited with no timeout at all).
     proc = fake_popen(_FakeProc(_FakeStream([]), _FakeStream(), wait_timeouts=1))
     with pytest.raises(RuntimeError, match="did not exit"):
-        edit.run_ffmpeg(["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: False)
+        edit.run_ffmpeg(
+            ["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: False
+        )
     assert proc.terminated
     # Two waits: the bounded grace wait that timed out, then _stop's own — never an unbounded one.
     assert proc.waits == 2
@@ -177,6 +184,8 @@ def test_stderr_is_drained_while_the_process_runs(fake_popen):
     # real pipe, an unread one fills at ~64KB and blocks ffmpeg's next write forever.
     err = _FakeStream([f"warning {i}\n" for i in range(500)])
     fake_popen(_FakeProc(_FakeStream(["out_time_us=1000000\n"]), err))
-    edit.run_ffmpeg(["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: False)
+    edit.run_ffmpeg(
+        ["ffmpeg"], total_s=10, on_progress=lambda _p: None, should_cancel=lambda: False
+    )
     assert err.consumed == 500
     assert err.closed