brand: social export pack + new og image and apple-touch icon

- assets/brand/: crest + plain-tachibana SVGs (stroked and flat-ink),
  1024px avatars, X header 1500x500, Etsy banner 1600x400, README with
  usage rules from the logo spec
- assets/og.png regenerated with the crest lockup (1200x630) — every
  page's share card updates with it
- apple-touch-icon.png (180px, matches the favicon) linked on all pages
- wordmark set in real Archivo 900 (fetched for render)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JWP9tY4m4hfX8WyoEEQ1kU

Author: claude

404.html

@@ -26,6 +26,7 @@
 <meta name="robots" content="noindex,follow">
 <meta name="theme-color" content="#43463e">
 <link rel="icon" href="/favicon.svg" type="image/svg+xml">
+<link rel="apple-touch-icon" href="/apple-touch-icon.png">
 <meta property="og:type" content="website">
 <meta property="og:site_name" content="PLOTFLOW">
 <meta property="og:title" content="Not found · PLOTFLOW*">

about.html

@@ -25,6 +25,7 @@
 <link rel="canonical" href="https://plotflow.io/about.html">
 <meta name="theme-color" content="#43463e">
 <link rel="icon" href="/favicon.svg" type="image/svg+xml">
+<link rel="apple-touch-icon" href="/apple-touch-icon.png">
 <meta property="og:type" content="website">
 <meta property="og:site_name" content="PLOTFLOW">
 <meta property="og:title" content="About · PLOTFLOW*">

apple-touch-icon.png

@@ -0,0 +1,25 @@
+# PLOTFLOW brand pack — 井筒に橘
+
+Colors: red #e8351f · olive #43463e · bristol #f6f3ec · ink #15160f
+
+## SVG (resolution-independent)
+- `plotflow-crest-stroked.svg` — primary mark. Stroked red; use on dark grounds.
+- `plotflow-crest-ink.svg` — flat ink form; use on paper/light grounds, print, seals.
+- `plotflow-tachibana-stroked.svg` / `-ink.svg` — plain 橘 (no frame), the
+  small-size form for 24–48 px display. Below 24 px use a text glyph.
+
+## PNG (socials, ready to upload)
+- `avatar-tachibana-1024.png` — **recommended avatar** (Instagram/Etsy/X).
+  Profile photos render tiny; plain 橘 stays legible where the framed
+  crest goes muddy.
+- `avatar-crest-1024.png` — full crest on olive, for contexts that show
+  the avatar large.
+- `banner-1500x500.png` — X/Twitter header (lockup, stroked on olive).
+- `banner-etsy-1600x400.png` — Etsy shop banner (flat ink on bristol).
+
+Site files (already wired): `/favicon.svg`, `/apple-touch-icon.png`,
+`/assets/og.png` (1200×630 share image).
+
+Rules (from the logo spec): the crest is the only red in a lockup; framed
+crest never below 48 px; no containers, gradients, or shadows; the
+literal * stays in running copy — the crest never replaces punctuation.