feat: Journal list, category pages, pagination, tokens and pl/en strings

- index and category pages paginate with ?page=N and 404 out of range
- category content renders above the list through the html gate
- related posts fall back to the latest posts
- --journal-* tokens and neutral base styles
- pl/en strings registered only for locales the app enables

app/components/Journal/RelatedPosts.vue

@@ -0,0 +1,14 @@
+<script setup lang="ts">
+// Related posts under a post. The page passes the API's related_posts, or
+// the latest posts when the post has no category.
+import type { JournalPost } from '../../utils/types.ts'
+
+defineProps<{ posts: JournalPost[] }>()
+</script>
+
+<template>
+  <section v-if="posts.length" class="journal-related">
+    <h2 class="journal-related__title">{{ $t('journal.post.related') }}</h2>
+    <JournalPostList :posts="posts" />
+  </section>
+</template>