Add the ihasmail theme, and make it the default

A dark theme carrying ihasmail.org's palette: a teal-navy ground rather
than the blue-slate of the plain dark theme, with the orange the logo's
cat is drawn in doing the work of the star and the warning colour. The
values are the site's own, read from its stylesheet rather than picked
by eye.

It is a theme rather than an accent because it changes backgrounds,
borders and text as well as the highlight -- an accent could not.

It rides on data-theme="dark" and adds data-palette="ihasmail" on top,
so the eleven dark-only rules further down the stylesheet keep applying
without being duplicated for a second dark theme. Specificity then does
something deliberate: the palette block is 0,2,0 and the accent variants
are 0,3,0, so a chosen accent still wins over it -- and because the
default accent ("teal") has no rule of its own, ihasmail.org's accent is
what shows until someone picks another. Verified both ways in a browser.

It is now what a new account starts on, so the app looks like itself
before anyone has chosen anything. Only a default: a stored theme always
wins, which leaves everyone already using ihasmail where they are, since
the setting is saved whether or not they deliberately picked it.

While here, the theme-color meta tag was fixed. There were two, both
carrying media attributes, and applyTheme looks for
:not([media]) -- so it matched neither and the browser chrome had never
followed the chosen theme at all, only what the OS preferred. One tag
now, updated from JS, starting at the default theme's background so the
first paint is right too.

Contrast measured rather than assumed, against the theme's own
background: text 14.5:1, muted 8.6:1, faint 6.4:1, accent 8.0:1, link
9.8:1, star 7.9:1, accent-on-accent 8.4:1. All AA or better.

web/src/styles/app.css

@@ -90,6 +90,59 @@
   color-scheme: dark;
 }
 
+/*
+ * The "ihasmail" theme: the palette from ihasmail.org, which is a teal-navy
+ * rather than the blue-slate of the plain dark theme, warmed by the orange the
+ * logo's cat is drawn in.
+ *
+ * It rides on data-theme="dark" rather than replacing it, so every dark-only
+ * rule further down this file -- tooltips, toasts, the message frame -- keeps
+ * applying without being duplicated. Only the palette is overridden.
+ *
+ * Specificity is doing deliberate work here. This block is [data-palette] plus
+ * :root, so 0,2,0; the accent variants below are :root[data-theme][data-accent],
+ * so 0,3,0 and they win. That is what makes the accent swatches keep working on
+ * top of this theme -- and because the default accent ("teal") has no rule of
+ * its own, ihasmail.org's own accent is what shows until someone picks another.
+ */
+:root[data-palette="ihasmail"] {
+  --bg: #0d2430;
+  --bg-elev: #12303e;
+  --bg-sunken: #0a1c26;
+  --bg-hover: rgba(70, 202, 195, 0.10);
+  --bg-active: rgba(70, 202, 195, 0.16);
+  --fg: #eaf6f6;
+  --fg-muted: #a3c3cb;
+  --fg-faint: #86aab4;
+  --border: #21505f;
+  --border-strong: #2e6a7a;
+  --accent: #46cac3;
+  --accent-fg: #062028;
+  --accent-soft: rgba(70, 202, 195, 0.16);
+  --accent-soft-fg: #9fe6e2;
+  --danger: #f87171;
+  --danger-soft: rgba(248, 113, 113, 0.15);
+  --warn: #f9a34b;
+  --warn-soft: rgba(249, 163, 75, 0.14);
+  --success: #4ade80;
+  --success-soft: rgba(74, 222, 128, 0.15);
+  --link: #6fdcd6;
+  --unread-bg: #163a4a;
+  --read-bg: #12303e;
+  --selected-bg: rgba(70, 202, 195, 0.18);
+  --focus-ring: 0 0 0 3px rgba(70, 202, 195, 0.4);
+  /* The cat is orange; so is the star. */
+  --star: #f9a34b;
+  --q1: #6fdcd6;
+  --q2: #4ade80;
+  --q3: #c084fc;
+  --scrollbar: rgba(163, 195, 203, 0.3);
+  --shadow-1: 0 1px 2px rgba(0, 0, 0, 0.45);
+  --shadow-2: 0 8px 24px rgba(0, 0, 0, 0.55);
+  --shadow-3: 0 22px 60px -28px rgba(0, 0, 0, 0.75);
+  color-scheme: dark;
+}
+
 /* Accent variants */
 :root[data-accent="blue"] { --accent: #2563eb; --accent-soft: #dbeafe; --accent-soft-fg: #1e3a8a; --selected-bg: #dbeafe; --focus-ring: 0 0 0 3px rgba(37,99,235,.35); --link:#1d4ed8; }
 :root[data-accent="purple"] { --accent: #7c3aed; --accent-soft: #ede9fe; --accent-soft-fg: #4c1d95; --selected-bg: #ede9fe; --focus-ring: 0 0 0 3px rgba(124,58,237,.35); --link:#6d28d9; }