feat: statuses and ticket types take any colour from a colour picker

Settings shows a native colour picker (the palette as suggestions)
instead of the list of eleven names. The API takes a palette name, as
before, or any #rrggbb; picking a palette colour still saves its name,
so it keeps its hand-made dark version. A free colour gets one variant
per theme, computed with the `color` library (moved towards white or
black until it contrasts 3:1 with the surface) and applied with
light-dark(): a pale yellow darkens on white, a navy lightens on dark.

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

package.json

@@ -49,6 +49,7 @@
     "chart.js": "^4.5.1",
     "class-transformer": "^0.5.1",
     "class-validator": "^0.15.1",
+    "color": "^5.0.3",
     "dompurify": "^3.4.16",
     "graphql": "^16.14.2",
     "graphql-redis-subscriptions": "^2.7.0",