App-icon tiles for Signals and DeadAir, drawn as the logo is (#268)

web/signals.svg and web/deadair-{on,off}.svg, each with a -dark twin,
follow logo.svg's rules: square and opaque, the logo's gradient ground,
flat layers in its scale blues, the needle's orange, nothing thin
enough to vanish at 32px. Signals is the page's own glyph, waves going
out from a point, the point in orange. DeadAir on is the waveform
closed up with the needle at the cut; off has the silence still in its
middle, an orange flat line, and its bars muted, so the state is in
the shape as the old glyphs had it.

The Signals folder row and its page header show the Signals tile in
place of the glyph on an accent tint; the player's DeadAir switch shows
the on or off tile. tile() puts both variants on the page, and the mode
rule that picked the logo's now picks any .onlight/.ondark. The three
glyphs nothing uses any more are gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/signals.svg

@@ -0,0 +1,17 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024">
+  <!-- The Signals folder's tile, drawn as logo.svg is (square, opaque, one background and flat
+       hard-edged layers, nothing thin enough to vanish at 32px) from the page's own Signals
+       glyph: waves going out from a point, the point in the needle's orange. Each <g> is a layer. -->
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#dff0fb"/>
+      <stop offset="1" stop-color="#9fccef"/>
+    </linearGradient>
+  </defs>
+  <g id="background"><rect width="1024" height="1024" fill="url(#bg)"/></g>
+  <g id="waves" fill="none" stroke="#2f6aa0" stroke-width="112" stroke-linecap="round">
+    <path d="M293 252A340 340 0 0 0 293 772M731 252A340 340 0 0 1 731 772" opacity=".5"/>
+    <path d="M377 351A210 210 0 0 0 377 673M647 351A210 210 0 0 1 647 673" opacity=".85"/>
+  </g>
+  <g id="point"><circle cx="512" cy="512" r="96" fill="#ff5500"/></g>
+</svg>