feat: add multi-language support to rss2bsky via --lang flag

- Changed `post_lang: str` to `post_langs: List[str]` in `run_once`
  and `try_send_post_with_variants` to support multiple BCP-47 language
  tags passed to Bluesky's `langs=` field.

- Updated `--lang` CLI argument to accept comma-separated language codes
  (e.g. `--lang ca,es`), parsed into a list at startup. Defaults to `["ca"]`.

- Added startup log line reporting the configured language(s) per run.

jenkins/crunchyRSS

@@ -51,7 +51,8 @@ pipeline {
                         "$BSKY_CRUNCHYROLL_HANDLE" \
                         "$TWITTER_CRUNCHY_EMAIL" \
                         "$BSKY_CRUNCHYROLL_APP_PASSWORD" \
-                        --service "https://eurosky.social"
+                        --service "https://eurosky.social" \
+                        --lang es
                     '''
                 }
             }