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.

blog/branding_prompt.md

@@ -1,6 +1,6 @@
 # Branding brief for SimurgArray
 
-Copy everything below the line into the branding agent.
+Copy everything below the line into a branding agent. The identity it asks for now exists in `branding/`; this brief is kept for future refinements.
 
 ________________________________________________________________________________
 
@@ -26,16 +26,13 @@ Precise, calm, honest, a little dry, quietly clever. Think of a well made scient
 
 ## Existing visual direction (keep and refine it, do not replace it)
 
-* **Core motif:** a bird in flight drawn only with round dots on a square grid, like beads on a BeadChip. The current bird faces right, wings raised and swept back, with a small crest, a hooked beak and three long tail plumes ending in round "peacock eye" dots.
-* **Channel colors:** the scanner has a red and a green channel. Dots on the outline of the bird are red and green; the inner dots, where both channels "overlap", are gold.
-* **Palette (starting point, you may tune values for contrast):**
-  * Channel red #C8453A
-  * Channel green #2F8F5B
-  * Simurg gold #D4A017
-  * Night indigo #1E2240 (backgrounds; most of the work happened at night)
-  * Paper #F7F5EF (documents, light backgrounds)
-* **Type so far:** Noto Sans for text, Noto Sans Mono for anything a user might paste into a terminal.
-* Five blog featured images already exist in this style (1200 x 630, indigo background, faint bead grid, bird on the right, title on the left, footer with three colored dots, the name and the tagline). Stay consistent with them.
+The identity already exists in `branding/` (guide: `branding/README.md`). Treat it as the starting point.
+
+* **Core motif:** a simurg seen from the front, wings raised in a V with three feathers each, a three dot crown, drawn only with round dots on a square grid like beads on a BeadChip. Three drawings: detailed (31 x 27 dots), simple (11 x 10) and micro (7 x 7).
+* **Channel colours:** the body, wings and crown are gold, "where the two channels meet". Three tail plumes: red on the left (red channel), gold in the middle, green on the right (green channel), each ending in a round peacock eye.
+* **Palette:** night indigo #1E2240, paper #F7F5EF, simurg gold #D4A017, gold deep #A87A00 (the bird on light backgrounds), gold ink #8C6500 (accent text on light), channel red #C8453A, channel green #2F8F5B, muted #A3A7C9 on dark and #5A5E7E on light. Charts use the Okabe and Ito colours with shapes.
+* **Type:** Noto Sans (wordmark in SemiBold, "Array" in the accent colour) and Noto Sans Mono.
+* The five blog featured images, the README banner, the social preview, the avatar and the HTML report header band already use it.
 
 ## Deliverables