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/IndexHeader.vue

@@ -0,0 +1,12 @@
+<script setup lang="ts">
+// Heading of the post index; pages after the first say which page they are.
+defineProps<{ page: number }>()
+</script>
+
+<template>
+  <header class="journal-index-header">
+    <h1 class="journal-index-header__title">
+      {{ $t('journal.index.title') }}<template v-if="page > 1"> · {{ $t('journal.pagination.pageTitle', { page }) }}</template>
+    </h1>
+  </header>
+</template>