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/base.css

@@ -61,6 +61,14 @@
   --tt-cyan:    #00ffff;
   --tt-white:   #ffffff;
 
+  /* A deliberate, acknowledged ninth: the fastext nav has eight
+     destinations and only five of the locked eight read as legible
+     text on black once red/green/yellow/cyan/magenta/blue are already
+     spoken for (Activity ran out — a dithered swatch alone read as
+     unfinished, and dithering the word itself was tried and found
+     illegible). Not "one of the eight" — used nowhere else. */
+  --tt-orange:  #ff8000;
+
   /* ── Roles ─────────────────────────────────────────────
      Each colour means one thing across all nine pages. */
   --ink:      var(--tt-white);   /* body text */