refactor(types): PEP-604 union sweep + UP007/UP045 enforcement

ruff --select UP007,UP045 --fix converted ~1760 sites across the
backend: `Optional[T]` → `T | None`, `Union[X, Y]` → `X | Y`. The
remaining module-level alias targets that ruff conservatively skips
(BindableFloatInput, ColorList, DeviceConfig) were converted by hand
earlier in the pass. black -formatted the result so the wider unions
fit cleanly under the 100-char line budget.

pyproject.toml now sets [tool.ruff.lint] extend-select = ["UP007",
"UP045"] so future legacy imports fire CI on every push. The
pre-commit ruff hook was bumped from v0.8.0 -> v0.15.12 to recognise
UP045 (split off from UP007 in v0.13).

server/tests/core/processing/test_effect_registry.py

@@ -17,7 +17,6 @@ from ledgrab.core.processing.effect_stream import (
     _effect_renderer,
 )
 
-
 EXPECTED_EFFECTS = frozenset(
     {
         "fire",

server/tests/core/processing/test_metric_readers.py

@@ -21,7 +21,6 @@ from ledgrab.core.processing.metric_readers import (
     get_spec,
 )
 
-
 EXPECTED_METRICS = {
     "cpu_load",
     "ram_usage",