feat(store): branded feature graphic (1024x500) + 512 store icon

Noto Sans wordmark on brand green (#2F7D34), white sprout, and the official
value tagline ('keep and share traditional seeds' / 'guarda y comparte...').
Generated by tool/gen_feature_graphic.py for en-US and es-ES.

apps/app_seeds/tool/gen_feature_graphic.py

@@ -0,0 +1,101 @@
+#!/usr/bin/env python3
+"""Generate Play Store feature graphics (1024x500) + store icon (512) for Tane.
+
+Brand green #2F7D34, white sprout from the adaptive foreground, 'Tane' wordmark
+in Noto Sans (the site's brand typeface), and the official value-proposition
+tagline. On-brand and replaceable with a designed asset later.
+
+Run from apps/app_seeds/:  python3 tool/gen_feature_graphic.py
+"""
+import os
+from PIL import Image, ImageDraw, ImageFont
+
+REPO_APP = "/home/vjrj/proyectos/dev/tane/.claude/worktrees/interesting-cray-6261fd/apps/app_seeds"
+NOTO = "/usr/share/fonts/truetype/noto"
+F_BOLD = f"{NOTO}/NotoSans-Bold.ttf"
+F_MED = f"{NOTO}/NotoSans-Medium.ttf"
+F_REG = f"{NOTO}/NotoSans-Regular.ttf"
+FG = f"{REPO_APP}/assets/icon_foreground.png"
+ICON = f"{REPO_APP}/assets/icon.png"
+
+GREEN = (47, 125, 52)       # #2F7D34
+GREEN_DARK = (34, 82, 30)   # #22521E
+WHITE = (255, 255, 255)
+FAINT = (208, 228, 210)
+
+W, H = 1024, 500
+
+# value line = what the app is (explains it); attrs = the differentiators.
+COPY = {
+    "en-US": ("Keep and share traditional seeds", "Offline   ·   Encrypted   ·   No account"),
+    "es-ES": ("Guarda y comparte semillas tradicionales", "Sin conexión   ·   Cifrado   ·   Sin cuenta"),
+}
+
+
+def sprout(height):
+    im = Image.open(FG).convert("RGBA")
+    bb = im.getbbox()
+    if bb:
+        im = im.crop(bb)
+    s = height / im.height
+    return im.resize((max(1, int(im.width * s)), height), Image.LANCZOS)
+
+
+def bg():
+    top = Image.new("RGB", (W, H), GREEN)
+    bot = Image.new("RGB", (W, H), GREEN_DARK)
+    mask = Image.new("L", (W, H))
+    md = ImageDraw.Draw(mask)
+    for y in range(H):
+        md.line([(0, y), (W, y)], fill=int(60 * (y / H)))
+    return Image.composite(bot, top, mask)
+
+
+def center_line(d, text, font, top, fill):
+    b = d.textbbox((0, 0), text, font=font)
+    w = b[2] - b[0]
+    d.text(((W - w) / 2 - b[0], top - b[1]), text, font=font, fill=fill)
+    return b[3] - b[1]
+
+
+def feature_graphic(locale, out):
+    img = bg()
+    d = ImageDraw.Draw(img)
+    value, attrs = COPY[locale]
+
+    # Row 1: sprout + 'Tane', centered as a group in the upper half.
+    spr = sprout(150)
+    wf = ImageFont.truetype(F_BOLD, 120)
+    wb = d.textbbox((0, 0), "Tane", font=wf)
+    ww, wh = wb[2] - wb[0], wb[3] - wb[1]
+    gap = 26
+    gw = spr.width + gap + ww
+    gx = (W - gw) // 2
+    row_top = 92
+    cy = row_top + spr.height / 2
+    img.paste(spr, (gx, row_top), spr)
+    d.text((gx + spr.width + gap - wb[0], cy - wh / 2 - wb[1]), "Tane", font=wf, fill=WHITE)
+    y = row_top + spr.height + 34
+
+    # Row 2: value proposition (explains the app).
+    vf = ImageFont.truetype(F_MED, 42)
+    y += center_line(d, value, vf, y, WHITE) + 18
+
+    # Row 3: differentiators, quieter.
+    af = ImageFont.truetype(F_REG, 30)
+    center_line(d, attrs, af, y, FAINT)
+
+    img.save(out, "PNG")
+    print("wrote", out, img.size)
+
+
+def store_icon(out):
+    Image.open(ICON).convert("RGB").resize((512, 512), Image.LANCZOS).save(out, "PNG")
+    print("wrote", out)
+
+
+for loc in ("en-US", "es-ES"):
+    d = f"{REPO_APP}/fastlane/metadata/android/{loc}/images"
+    os.makedirs(d, exist_ok=True)
+    feature_graphic(loc, f"{d}/featureGraphic.png")
+    store_icon(f"{d}/icon.png")