A UI pass: contrast in every theme, and a sign-in page that fits

Measured every theme's palette against WCAG AA. The unread badge's count
on its --accent2 fill fell as low as 2.6:1 (Flat Remix light), and the
unread dot with it; each theme's --accent2 is taken down until white on
it clears 4.5. Tags were --warn or --bad on --raise, short of AA in most
light themes, so they are outlined on the row's own ground instead.

Nordic dark had --line equal to --panel2, so bordered buttons on a
panel2 ground drew no edge at all. Classic's selected row left the
row's icon buttons grey on the blue. A zero badge on a selected row was
--raise on --raise and vanished.

login.html never had a doctype or viewport meta, so it rendered in
quirks mode and at desktop width on a phone, and its light palette sat
under data-theme="light", which nothing ever set. It follows
prefers-color-scheme now, signed out having no account to ask.

Dropped the unused log and users icons. The Classic theme's label is
now just "Classic".

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

web/src/theme.ts

@@ -6,7 +6,7 @@
 // the system, so no palette is written twice.
 const THEMES: Record<string, {name: string, modes: boolean}> = {
   modern: {name: 'Modern', modes: true},
-  classic: {name: 'Classic, the 2004 Mac app', modes: false},
+  classic: {name: 'Classic', modes: false},
   dracula: {name: 'Dracula', modes: true},
   material: {name: 'Material', modes: true},
   adwaita: {name: 'Adwaita', modes: true},