Apply the brand across the repo: reports, README, guide

* simurg/core/brand.py: single source of the mark geometry, colours, favicon
  and the report header band (scripts/brand now load it from there).
* HTML reports (QC report, compare dashboard, methylation QC): offline SVG
  favicon, indigo header band with the mark, version and a sha256 of the data
  shown; Noto Sans font stack; methylation plots in Okabe-Ito colours.
* README banner, guide logo, brand/blog links; branding brief updated to the
  final identity; Noto (OFL) and Okabe-Ito entries in THIRD_PARTY_NOTICES;
  CHANGELOG (Unreleased).

Unit tests + P5 QC oracle: 285 passed; ruff and mypy clean.

docs/user_guide.md

@@ -1,3 +1,5 @@
+<img src="../branding/logo/png/lockup_horizontal_light.png" alt="SimurgArray" width="360">
+
 # SimurgArray user guide (v2.0)
 
 SimurgArray turns Illumina Infinium genotyping BeadChip scans (IDAT files) into genotype calls, QC tables and