[bug] Language filter 'All' option reverts to English

[realproject7]

Bug

When the user selects "All languages" from the language filter dropdown, the page reloads but reverts back to "English." Users cannot browse stories in all languages.

Root Cause

PR #270 changed the language fallback in src/app/page.tsx from "all" to "English":

const lang = rawLang && (LANGUAGES as readonly string[]).includes(rawLang) ? rawLang : "English";

The problem: when the user selects "All languages", the GenreLanguageFilter component sets lang to "all" in the URL params. But "all" is not in the LANGUAGES array, so the validation rejects it and falls back to "English".

Fix

In src/app/page.tsx, allow "all" as a valid lang value:

const lang = rawLang === "all" ? "all" : rawLang && (LANGUAGES as readonly string[]).includes(rawLang) ? rawLang : "English";

This preserves the default-to-English behavior (no lang param → English) while still allowing explicit ?lang=all to show all languages.

Files to modify

• src/app/page.tsx — allow "all" as valid lang param

Acceptance criteria

• No lang param in URL → defaults to English (existing behavior)
• ?lang=all → shows all languages
• Selecting "All languages" from dropdown works and persists
• npm run typecheck passes