Give Activity a genuine ninth colour: --tt-orange

Requested directly: "can we make activity orange". The locked eight
palette had already run out at six legible text colours (Watch's blue
was the last one, and it's already a contrast exception); a dithered
swatch alone read as unfinished, and dithering the word itself
rendered as illegible static — tried and reverted this session.

--tt-orange (#ff8000) is defined in base.css right after the locked
eight, clearly marked as a deliberate, acknowledged one-off exception
to "eight colours, no ninth" rather than a secretly-smuggled-in tint.
Same flat text+swatch treatment as every other fastext key. Updated
CLAUDE.md's discipline 1 and DESIGN.md's Locked Eight Rule to name the
exception explicitly, so it reads as a documented decision next time
someone audits the palette, not a bug.

static/css/teletext.css

@@ -533,9 +533,7 @@ a.tt-row:focus-visible .tt-row-sub { color: var(--tt-black); }
   text-overflow: ellipsis;
 }
 /* The key's identity is carried by a cell at its head — the physical
-   coloured button on the remote. Solid for most; k-blue and k-dither
-   override its background below, since a flat swatch can't carry
-   every one of the eight destinations without repeating a colour. */
+   coloured button on the remote. */
 .fastext a > span, .fastext-here > span {
   min-width: 0;
   overflow: hidden;
@@ -564,10 +562,9 @@ a.tt-row:focus-visible .tt-row-sub { color: var(--tt-black); }
    other body text in this app clears — but the word carries the
    colour like every other key here, at the visitor's request. */
 .fastext .k-blue { color: var(--field); }
-/* The one other legal way to get a distinct mark out of eight colours
-   without a ninth: an ordered dither, same mechanism as --dither-mid,
-   in place of a flat swatch. */
-.fastext .k-dither::before { background: var(--dither-mid); }
+/* --tt-orange is a genuine ninth colour, not one of the locked eight —
+   see its definition in base.css for why the palette ran out here. */
+.fastext .k-orange { color: var(--tt-orange); }
 .fastext a:hover, .fastext a:focus-visible {
   background: currentColor;
   outline: none;