Move talks, teaching and software to data files; richer publication links

[sbryngelson]

Summary

Phase 3 of the template cleanup: the data model. Users edit YAML lists and BibTeX fields instead of HTML.

Publications

• Links from BibTeX fields: file (PDF), doi, arxiv, url, code, slides, video, poster, data each become a pill button. The old convention (arXiv id in doi for @unpublished) still works. Template-only fields are stripped from the copyable BibTeX.
• BIB button on every entry type (was five types only).
• Year badge from entry.year in the template, replacing the JS regex over citation text.
• selected = {true} lists an entry in a "Selected publications" block on the home page; the block hides itself when nothing is flagged.
• citesty.csl no longer prints URLs inside reference text (links are buttons; its DOI branch had already been removed for the same reason).

Data-driven pages

• _data/talks.yml replaces the @incollection[keywords ^= invited] BibTeX hack (invited/contributed sections, optional link/slides/video buttons).
• _data/teaching.yml and _data/software.yml drive the Teaching and Software pages.
• _data/people.yml and the About page's duplicate "Students and Mentoring" list are removed (agreed in review of the design).
• Empty lists render a short hint pointing at the data file.

Setup and configuration

• ./setup.sh --clean strips the Feynman demo (data entries, ref.bib, posts, papers, demo images, prose) to commented skeletons plus a placeholder avatar, then runs the usual prompts; prompts also set description and derive scholar.last_name / first_name. This is the permanent answer to "Remove (me) Spencer!" (Remove (me) Spencer! #3).
• Analytics: Plausible, Umami, GoatCounter alongside GA4, one line each.
• nav_pages[].label for navbar text that differs from the URL.

Verification

• Acceptance script: BIB on all 14 entries, server-rendered badges, arXiv/Code/Slides buttons, stripped BibTeX fields, no "Retrieved" text; selected block with the 3 flagged entries; talks 4 invited + 6 contributed with buttons and date text; teaching 4 courses; software 2 cards; nav label and Plausible/GoatCounter emission checked via a config overlay build.
• setup.sh --clean exercised end-to-end in a scratch copy: exits 0, config rewritten (name, scholar names, description, placeholder photo, blank links), demo files gone, data files comment-only, clean site builds with zero occurrences of "Feynman", empty-state hints shown, favicon initials "JS".
• Browser test (puppeteer, 22 checks) still passes; Lighthouse accessibility and best-practices 100 on home, talks, teaching, software, publications.

Upgrading

UPGRADING.md covers the talks migration, removed people.yml, and the new BibTeX fields.