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.

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## Unreleased
+
+**Branding.** A visual identity (`branding/`, guide in `branding/README.md`): a dotted simurg mark in detailed, simple
+and micro drawings, wordmark and lockups, icons, README banner, social preview and featured-image templates, with
+contrast and colour-vision checks. HTML reports (QC report, compare dashboard, methylation QC) get a favicon and a
+header band with the mark, the software version and a checksum of the data they show. The mark geometry lives in
+`simurg/core/brand.py`. Blog posts and featured images in `blog/`.
+
 ## 2.0.0 — 2026-09-30 (v2 modules)
 
 The Python package is 2.0.0. The optional Rust kernels are unchanged and stay `simurg_core` 1.1.0.