Branding, Excel watermark, live run progress, and uv

- Login and Reports pages: eCare logo, Waystar and Aquilaehr logos (light
  versions for the dark pages), eCare favicon.
- Excel reports: faded eCare/Waystar/Aquila watermark as the sheet
  background on both sheets. Report writer moves to xlsxwriter, the only
  engine that can set a sheet background.
- Reports page: animated run progress (both download lanes piped into the
  Excel sheet) and a plain-language activity feed built from the run log;
  the raw log stays under "Technical log". /status now returns the
  location count.
- Dependencies move from requirements.txt to pyproject.toml + uv.lock;
  Dockerfile installs uv from PyPI and runs uv sync --frozen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,12 @@
+[project]
+name = "mek-charge-reconciliation"
+version = "0.1.0"
+description = "Waystar vs Aquilaehr charge reconciliation, per location, with a small web front end"
+requires-python = ">=3.12"
+dependencies = [
+    "flask==3.1.0",
+    "gunicorn==23.0.0",
+    "pandas==3.0.3",
+    "playwright==1.49.0",
+    "xlsxwriter==3.3.0",
+]