feat(blog-share): mirror blog_share_base.css + Ash share theme; fix Cookie @font-face placeholder

- base.css: @font-face Cookie now points at the real font note id (was the unresolved
  __COOKIE_FONT_ID__ placeholder -> 404 -> BMC button fell through to serif)
- base.css: removed selectorless declaration block (dead code from a lost selector),
  merged the intended a.blog-subcategory gap rule into the existing block
- README: document blog-share/ and note that Trilium code notes remain source of truth

README.md

@@ -74,6 +74,24 @@ Installation (Gitea 1.27+):
 
 3. Restart Gitea, then pick the theme from **Explore → Preferences → UI theme**.
 
+## Blog share themes (same palettes)
+
+The public blog (`richard.familie-zink.org`) runs on Trilium's share feature with a custom EJS
+template; its frontend styling lives in two note-based stylesheets, mirrored here:
+
+| File | Role |
+|---|---|
+| `blog-share/blog_share_base.css` | Layout/shared widgets (posts, search, pagination, BMC box, code blocks, scrollbars) – theme-independent, driven by the `--*` variables below |
+| `blog-share/blog_share_theme_ash.css` | Ash palette for both `html.theme-light` / `html.theme-dark`, incl. all Mermaid chart-type rules |
+
+Notes:
+
+- **Source of truth** is the matching Trilium code notes (`.blog` folder) which the share links via
+  `shareCss`; this repo copy is the backup/mirror. Copy changes back and forth deliberately.
+- The `@font-face` for the "Cookie" handwriting font (Buy-Me-a-Coffee button) resolves against a
+  live Trilium **file note id** (`/api/notes/<id>/download`) – it only works when served from the
+  same Trilium instance; the mirrored file contains the real id of this instance.
+
 ## Customising
 
 The themes are variable-driven. Edit the `--*` values inside the `#trilium-app { ... }` block and the