Let a selection show through an inline code chip

Selecting a sentence highlighted every word of it except the ones in
backticks. An inline span's background is part of the text's own drawing
and the selection rectangle is drawn underneath it, so an opaque chip hid
the selection completely -- and there is no way to draw it over instead,
since the order is the text node's. The chip's fill is 60% now: measured on
the emulator, unselected it is #161622 against a #1E1E2E page, so it is
still a clear step down, and selected it moves to #3C344F, which is the
whole point.

This is what Iris's screenshot was showing. A fenced block was never
affected -- its background is on the box around the text rather than on
spans, so the selection lands on top of it, which is why it looked fine
when I went looking.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

TODO.md

@@ -5,14 +5,6 @@ one in place when it turns out to need a decision.
 
 ## App — transcript
 
-- [ ] Text inside code blocks does not highlight when selected. **Measured, and
-      it does** — the selection is drawn, but over the near-black surface a code
-      block and a tool's output sit on, Material's default 40%-alpha tint
-      composites to a barely-there smudge, much weaker than the same selection
-      over a reply. The app now states its own selection colours
-      (`AiAppSelectionColors`), which took the fill from #5B4C73 to #776394 on
-      that surface. Worth confirming this was the complaint rather than a
-      selection that draws *nothing* on the phone.
 - [ ] Messages received from other agents are inconsistent — sometimes they
       appear, sometimes they don't. **Needs a rig.** Read the code rather than
       measured: a live Claude session only learns of a peer message from the