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>

Dockerfile

@@ -6,3 +6,6 @@ RUN apt-get update -qq \
 
 COPY pipelines/songs/requirements.txt /tmp/songs-requirements.txt
 RUN pip install --no-cache-dir -r /tmp/songs-requirements.txt
+
+COPY pipelines/ses/requirements.txt /tmp/ses-requirements.txt
+RUN pip install --no-cache-dir -r /tmp/ses-requirements.txt