Add pluggable metrics architecture with LUFS

Introduce a Metric ABC (compute on worker thread, render on GUI thread)
with a METRICS registry, and refactor the analysis pipeline around it.
RMS power (ported), raw waveform, and BS.1770 LUFS (via pyloudnorm) ship
as the initial three; new metrics drop in by appending to METRICS.

- metrics.py: Metric ABC + RMSPowerMetric, WaveformMetric (locked to
  +/-1.1 y-range for float headroom), LUFSMetric (short-term 3 s window
  + integrated value, with streaming-target reference line).
- plot_control_widget.py: metric selector dropdown + Refresh Plot button
  (moved out of FontControlWidget).
- analysis_results_manager.py: AnalysisResult caches the AudioFile and a
  per-metric data dict; new MetricComputeWorker runs metric switches off
  the GUI thread via metricComputeStarted/metricReady/metricComputeError
  signals, so LUFS on a 12-minute track no longer stalls the UI.
- main.py: all redraw paths funnel through one _render_or_request helper;
  stale-result guards keep slow computes from overwriting fresh selections.
- plotting_engine.py removed (metadata text moved onto AnalysisResult;
  figure construction lives in each Metric).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

uv.lock

@@ -1187,6 +1187,21 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/0c/c3/44f3fbbfa403ea2a7c779186dc20772604442dde72947e7d01069cbe98e3/pycparser-3.0-py3-none-any.whl", hash = "sha256:b727414169a36b7d524c1c3e31839a521725078d7b2ff038656844266160a992", size = 48172, upload-time = "2026-01-21T14:26:50.693Z" },
 ]
 
+[[package]]
+name = "pyloudnorm"
+version = "0.2.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "numpy", version = "2.2.6", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.11'" },
+    { name = "numpy", version = "2.4.6", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.11'" },
+    { name = "scipy", version = "1.15.3", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.11'" },
+    { name = "scipy", version = "1.17.1", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.11'" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/23/00/f915eaa75326f4209941179c2b93ac477f2040e4aeff5bb21d16eb8058f9/pyloudnorm-0.2.0.tar.gz", hash = "sha256:8bf597658ea4e1975c275adf490f6deb5369ea409f2901f939915efa4b681b16", size = 14037, upload-time = "2026-01-04T11:43:35.265Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/aa/b6/65a49a05614b2548edbba3aab118f2ebe7441dfd778accdcdce9f6567f20/pyloudnorm-0.2.0-py3-none-any.whl", hash = "sha256:9bb69afb904f59d007a7f9ba3d75d16fb8aeef35c44d6df822a9f192d69cf13f", size = 10879, upload-time = "2026-01-04T11:43:34.534Z" },
+]
+
 [[package]]
 name = "pyparsing"
 version = "3.3.2"
@@ -1642,6 +1657,7 @@ dependencies = [
     { name = "mutagen" },
     { name = "numpy", version = "2.2.6", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.11'" },
     { name = "numpy", version = "2.4.6", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.11'" },
+    { name = "pyloudnorm" },
     { name = "pyqt5" },
     { name = "pyqt5-qt5", marker = "sys_platform == 'win32'" },
 ]
@@ -1652,6 +1668,7 @@ requires-dist = [
     { name = "matplotlib" },
     { name = "mutagen" },
     { name = "numpy" },
+    { name = "pyloudnorm" },
     { name = "pyqt5", specifier = ">=5.15.10" },
     { name = "pyqt5-qt5", marker = "sys_platform == 'win32'", specifier = "==5.15.2" },
 ]