feat: tsuki Firefox theme for Nova (157+)

Adaptive light/dark static theme generated from @tsuki/tokens, plus an
optional userChrome.css layer (IBM Plex, tsuki radii, shu accent) that
overrides Nova's design tokens. Self-hosted via AMO unlisted signing and
Gitea releases.

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

biome.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "https://biomejs.dev/schemas/1.9.0/schema.json",
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "indentWidth": 2,
+    "lineWidth": 100
+  },
+  "javascript": {
+    "formatter": {
+      "quoteStyle": "single"
+    }
+  },
+  "files": {
+    "ignore": ["dist", "node_modules"]
+  }
+}