Link commemorations to their full stories below the readings

[brianglass]

Summary

• Each saint/feast in the top-of-page commemorations list now links to its corresponding full story further down the page (in the section following the scripture readings), when one exists.
• Day.saint_links (new, in calendarium/liturgics/day.py) pairs each title with its DayCommemoration id (or None) in parallel with self.saints -- self.saints itself is untouched, since it's also consumed as plain strings elsewhere (ical.py, RSS feed description).
• Story-less commemorations (the antiochian.org bulk-harvested entries from the previous PR) render as plain text, same as before -- there's nothing to link to.
• Added .commemorations li a CSS so the new links inherit the existing red color/no-underline styling instead of the browser's default blue/underlined link style (the readings page doesn't use the #content wrapper that already had link styling elsewhere on the site).

Test plan

• Full test suite passes (120/120)
• Verified live on the dev server: Jan 1 (both commemorations have stories and link correctly) and July 29 in Greek tradition (2 linked, 5 plain-text for story-less entries)
• No further cross-browser/visual check done in this session

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