Name the icons by their contents in the pages (#57)

/favicon.png, /apple-touch-icon.png and /logo.svg are kept a day under
fixed names, so after the new logo went out, curl through the tunnel and
browsers still got the old one. The pages now ask for them as
/favicon.png?v=<hash>, the way they already ask for app.js and app.css,
so a changed icon is a new URL for every cache on the way. /favicon.ico
cannot carry a query, as browsers ask for it on their own; it keeps the
day.

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

CHANGELOG.md

@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- A new tab or home-screen icon shows up as soon as it is deployed, instead of a day later.
 - Opened from the home screen on an iPhone, the top bar, the reader's back button and the top
   of the feed list keep clear of the Dynamic Island and the status bar instead of sitting under
   them.