feat(rhema-code): add the colors setting with four palettes

The stored `colors` key names a palette — rhema (the default,
Jadeite), aquamarine, black-and-white, or dracula — and the
Appearance page of /settings cycles it live, like the theme and
icon toggles beside it. Each palette carries a dark and a light
appearance under the existing `theme` key; dracula's light side is
derived, the official palette ships only dark.

The appearance decision moves off token comparison: Theme now
answers is_dark() from the ground/text luminance, so palettes
beyond the original two get the right per-profile fallback tones.

web/claw/app/components/SettingCard.vue

@@ -0,0 +1,21 @@
+<script setup lang="ts">
+// One titled card of setting rows or static facts — the repeating
+// surface of every settings page. The header may carry a meta note on
+// the right ("4 unset — inherit the primary model"-style).
+defineProps<{
+  title: string
+  meta?: string
+}>()
+</script>
+
+<template>
+  <section class="card">
+    <header class="card-head">
+      <span class="title">{{ title }}</span>
+      <span v-if="meta || $slots.meta" class="meta"><slot name="meta">{{ meta }}</slot></span>
+    </header>
+    <div class="card-body">
+      <slot />
+    </div>
+  </section>
+</template>