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/AppMarkdown.vue

@@ -0,0 +1,36 @@
+<script setup lang="ts">
+// Agent replies are markdown; this mounts the rendered HTML. The parser
+// keeps raw HTML in the source escaped (html stays false) and refuses
+// javascript: link targets, so v-html only ever receives generated
+// markup.
+import MarkdownIt from 'markdown-it'
+import type { RendererRule } from 'markdown-it'
+
+const props = defineProps<{
+  text: string
+  /** While true, a blinking cursor trails the last rendered block. */
+  streaming?: boolean
+}>()
+
+const md = new MarkdownIt({ html: false, linkify: true })
+
+// Rendered links leave the dashboard; open them in a new tab so the
+// transcript and its event stream survive the click.
+const defaultLinkOpen: RendererRule =
+  md.renderer.rules.link_open ??
+  ((tokens, idx, options, env, self) => self.renderToken(tokens, idx, options))
+md.renderer.rules.link_open = (tokens, idx, options, env, self) => {
+  const token = tokens[idx]
+  if (token) {
+    token.attrSet('target', '_blank')
+    token.attrSet('rel', 'noopener noreferrer')
+  }
+  return defaultLinkOpen(tokens, idx, options, env, self)
+}
+
+const html = computed(() => md.render(props.text))
+</script>
+
+<template>
+  <div class="md" :class="{ streaming }" v-html="html" />
+</template>