feat(ses): add SES light novel pipeline; extract shared lib/wiki.py

New pipeline at pipelines/ses/ publishes mikkeli/ses-light-novel to
the SES: MediaWiki namespace. All pages get Category:SES and
Category:SES:<type> (type from frontmatter, fallback to parent dir name).

Shared functions (connect_wiki, markdown_to_wikitext, strip_first_h1,
AUTO_BANNER_PREFIX) extracted from songs/publish.py into lib/wiki.py;
songs refactored to import from there.

Also adds publish-ses.yml workflow stub and updates Dockerfile and
root README.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pipelines/ses/requirements.txt

@@ -0,0 +1,3 @@
+python-frontmatter
+mwclient
+PyYAML