feat: add dynamic gist language sidebar filtering based on existing database entries

Add a new `get_gist_languages()` function in database.py that queries distinct language codes from the gists table and caches results for 60 seconds. Create a database index on the `language` column of the gists table for efficient queries. Update the gists router to pass the set of active language codes to the template. Modify the gists.html sidebar to only display language filter links for codes that actually have gists in the database, hiding empty language categories and conditionally showing the plaintext link.

devplacepy/routers/gists.py

@@ -4,7 +4,7 @@ from datetime import datetime, timezone
 from fastapi import APIRouter, Request, HTTPException, Form
 from devplacepy.models import GistForm, GistEditForm
 from fastapi.responses import HTMLResponse, RedirectResponse
-from devplacepy.database import get_table, get_users_by_uids
+from devplacepy.database import get_table, get_users_by_uids, get_gist_languages
 from devplacepy.content import load_detail, edit_content_item, delete_content_item, enrich_items
 from devplacepy.templating import templates
 from devplacepy.utils import generate_uid, get_current_user, require_user, make_combined_slug, create_mention_notifications
@@ -65,6 +65,7 @@ async def gists_page(request: Request, language: str = None, user_uid: str = Non
         "total_count": total_count,
         "current_language": language,
         "languages": LANGUAGES,
+        "gist_language_codes": get_gist_languages(),
     })