feat(brand): Minstrel mark — favicon, header lockup, Android adaptive icon

A Didone M whose right leg is an eighth note: stem, flag and notehead in the
accent, the letter in parchment. Traced from the operator's reference at
99.74% IoU (potrace, 26 + 22 segments), so the geometry is theirs, not an
approximation of it.

Subject-neutral on purpose. "Minstrel" pulls toward a lute or a bard, which
would tell a new user this is a renaissance-faire player rather than one for
all music. A geometric letter plus universal notation says "music" without
saying which music. The family look arrives through palette and drawing
style instead of through the subject — see the design-system discussion.

Starting state: web/static/favicon.png was a 1x1 PIXEL placeholder, so there
was effectively no favicon at all; Android had legacy bitmaps only, so modern
launchers letterboxed the square instead of masking it.

## The colour problem, and why each surface differs

Parchment on white is invisible — the operator caught this. The M therefore
has to flip with its background, while the accent note holds in both:

  - mark.svg / MinstrelMark.svelte use currentColor, so the letter takes the
    surrounding text colour and one asset covers both palettes.
  - favicon.svg bakes colours with a prefers-color-scheme swap, because a
    favicon sits on browser chrome and has no cascade to inherit from.
  - PNG fallback, apple-touch-icon and Android are PLATED. A PNG can't
    respond to scheme and iOS composites onto white regardless.

MinstrelMark is inlined rather than <img src>, because an <img> cannot
inherit currentColor and inheriting it is the entire point.

## Plate colour chosen by measurement

Obsidian (#14171A), not the raised-surface iron. The accent note only clears
the 3:1 non-text contrast threshold against the darker value: 3.04:1 vs iron's
2.70:1. My own earlier suggestion — lighten the plate — is WRONG and the
numbers say so: slate scores 2.21:1, worse, because the note is a dark colour
and lifting the plate closes the gap. Recorded in colors.xml so the reasoning
sits with the value.

## Construction

Traced as a full ink silhouette with the note painted OVER it, rather than as
two separate shapes. Separate shapes needed either a 2px seam where letter and
note touch, or an anti-aliasing fringe (2,430 misclassified pixels) around the
note. Painting over avoids both and yields a monochrome version for free — the
base layer alone is the whole mark in one colour, which is what
mipmap-anydpi-v26's <monochrome> uses for themed icons.

Android foreground sits at 61% of the 108dp canvas so it stays inside the
66dp safe zone and no launcher mask can clip it.

Paths are duplicated between the component and the two static SVGs, since one
needs currentColor and the others need literals. A comment in each names the
others.

Verified by render at 16/20/32/64/180 on obsidian, white, parchment and
plated; one optical size holds across the whole range.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

android/app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Adaptive icon (API 26+). Before this the app shipped legacy bitmaps only,
+     so modern launchers letterboxed the square instead of masking it to the
+     device's icon shape. The foreground PNGs are drawn on a 108dp canvas with
+     the mark inside the 66dp safe zone, so no mask can clip it. -->
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/ic_launcher_background"/>
+    <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
+    <monochrome android:drawable="@mipmap/ic_launcher_foreground"/>
+</adaptive-icon>

android/app/src/main/res/values/colors.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Obsidian. The adaptive icon's plate; chosen over the raised-surface
+         iron because the accent note only clears the 3:1 graphics contrast
+         threshold against this darker value (3.04:1 vs 2.70:1). -->
+    <color name="ic_launcher_background">#14171A</color>
+</resources>