feat(01-12): wave-2 task-1 — rasterize Loom mark to icons/icon{16,48,128}.png (overwrites Bug A placeholders)

scripts/rasterize-icons.sh (80 lines) is the one-off rasterization
recipe. It reads src/shared/brand/mokosh-mark.svg and emits the three
toolbar icon sizes via rsvg-convert, with assets-spec.md size FLOOR
sanity checks embedded.

Before:
  icons/icon16.png  574 B  16-bit/color RGB     (Bug A placeholder)
  icons/icon48.png  1153 B 16-bit/color RGB     (Bug A placeholder)
  icons/icon128.png 2615 B 16-bit/color RGB     (Bug A placeholder)

After:
  icons/icon16.png  406 B  8-bit/color RGBA     (Loom mark — D-01)
  icons/icon48.png  784 B  8-bit/color RGBA     (Loom mark — D-01)
  icons/icon128.png 1952 B 8-bit/color RGBA     (Loom mark — D-01)

All three clear assets-spec.md Chrome imageUtil silent-rejection floors
(16≥200B, 48≥500B, 128≥1024B). Sizes match RESEARCH §3 verification.

Per D-06 (Neutral mark + dynamic badge): single neutral mark per size;
no per-state PNG sets. The dynamic chrome.action.setBadgeBackgroundColor
in src/background/index.ts does state communication via colored badge.

Per RESEARCH §3 anti-pattern: PNGs are COMMITTED as static artifacts;
not regenerated at build time. scripts/rasterize-icons.sh is the
documented re-run recipe (for when src/shared/brand/mokosh-mark.svg
changes).

Verification:
- tests/build/icons-present.test.ts: 15/15 GREEN (existence, FLOOR,
  PNG signature, dimensions, color-type byte === 6 RGBA)
- Bug A regression check: file content differs from prior placeholders
  (verified via git diff binary status); the placeholder fingerprint
  used by harness A19 (Wave 6) will distinguish on first 32 bytes.

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

scripts/rasterize-icons.sh

@@ -0,0 +1,79 @@
+#!/usr/bin/env bash
+#
+# scripts/rasterize-icons.sh — Plan 01-12 Wave 2 Task 1.
+#
+# One-off icon rasterization recipe.
+#
+# Reads src/shared/brand/mokosh-mark.svg (the Loom 2×2 weave intersection
+# brand mark; D-01) and emits icons/icon{16,48,128}.png via rsvg-convert.
+#
+# Verified locally (RESEARCH §3): output is 8-bit/color RGBA, non-
+# interlaced PNG at the requested dimensions. Sizes clear assets-spec.md
+# Chrome imageUtil floors (16≥200B, 48≥500B, 128≥1024B):
+#   16  → ~406 B
+#   48  → ~784 B
+#   128 → ~1952 B
+#
+# This script is NOT wired into prebuild (per RESEARCH §3 anti-pattern:
+# regenerating icons at every build is wasteful + masks regressions in
+# the source SVG). PNGs are committed as static artifacts; re-run this
+# script when src/shared/brand/mokosh-mark.svg changes.
+#
+# Replaces the Bug A Plan 01-09 Path A placeholder icons (16-bit/color
+# RGB dark-square + green-dot at 574 B / 1153 B / 2615 B) with the
+# rasterized Loom mark.
+#
+# References:
+#   - librsvg rsvg-convert(1) manpage
+#   - assets-spec.md Chrome imageUtil silent-rejection floors
+#   - Plan 01-12 RESEARCH §3 (rsvg-convert default output format)
+#
+# Google bash style applies; see https://google.github.io/styleguide/shellguide.html
+
+set -euo pipefail
+
+readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+readonly REPO_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+readonly MARK_SVG="${REPO_ROOT}/src/shared/brand/mokosh-mark.svg"
+readonly ICONS_DIR="${REPO_ROOT}/icons"
+
+# Per assets-spec.md silent-rejection floors. Indexed by size for clear logs.
+declare -rA FLOORS=(
+  [16]=200
+  [48]=500
+  [128]=1024
+)
+
+main() {
+  if [[ ! -f "${MARK_SVG}" ]]; then
+    echo "ERROR: ${MARK_SVG} not found" >&2
+    return 1
+  fi
+  if ! command -v rsvg-convert >/dev/null 2>&1; then
+    echo "ERROR: rsvg-convert not found on PATH (install librsvg)" >&2
+    return 1
+  fi
+
+  mkdir -p "${ICONS_DIR}"
+
+  local size
+  for size in 16 48 128; do
+    local out="${ICONS_DIR}/icon${size}.png"
+    rsvg-convert -w "${size}" -h "${size}" "${MARK_SVG}" -o "${out}"
+
+    local bytes
+    bytes="$(stat -c%s "${out}")"
+    local floor="${FLOORS[${size}]}"
+
+    if (( bytes < floor )); then
+      echo "FAIL: ${out} (${bytes} bytes) is below Chrome imageUtil floor ${floor} B" >&2
+      return 1
+    fi
+    echo "  rasterized: ${out} (${bytes} bytes; floor ${floor} B)"
+  done
+
+  echo
+  echo "==> Done. PNGs are at ${ICONS_DIR}/icon{16,48,128}.png."
+}
+
+main "$@"