feat(icon): line-art cal + calendula bloom + numeral "1"

Replaces the simple numeral-only foreground from v0.1.0. The new mark
keeps the kalendae reference explicit (a bold "1" inside the
calendar body) and adds a small calendula bloom as a badge in the
bottom-right corner so the app's "calendula" brand reads at first
glance.

- design/icon/calendula_mark.svg: source SVG (232x232 viewport,
  monochrome, lawnicons-style strokes 12/8)
- app/src/main/res/drawable/ic_launcher_foreground.xml: regenerated
  as a VectorDrawable preserving the source path data. Off-white
  (#FAF6F0) strokes on the existing slate background. Reused as the
  <monochrome> slot so Android 13+ themed-icon launchers can recolor
  it from wallpaper.
- fdroid-metadata/.../{en-US,de-DE}/icon.png: 512x512 PNG composed
  from the same source SVG with the slate background baked in, so
  F-Droid clients show a fully rendered tile in the app catalog.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

design/icon/calendula_mark.svg

@@ -0,0 +1,13 @@
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