Merge origin/main into branch — structure stays…

Details

Bring this branch up to date with main while preserving the SCSS
modularization done here.
Per the user's rule: structure comes from this branch, file contents
come from main (since main has the updated versions).
Resolution:
- Files only main changed (CLAUDE.md, db_assets.ts, seasonal-background.ts,
  snow-gl.ts, _includes/v2/experience.html, teaching_talks.html): taken
  verbatim from main via the auto-merge.
- _sass/v2.scss (touched on both sides): kept this branch's @import
  manifest. Re-sliced main's updated single-file content into the same
  per-partial layout. Concrete net effect:
    * _prose.scss: gained the new .v2-card block.
    * _records.scss: shrunk to just the two-column block (main deleted
      the old .v2-education-grid/.v2-experience .v2-timeline block as
      the items are now boxed via .v2-card).
    * _responsive.scss: gained .v2-card in the bg-card media query.
Verified with dart-sass: every front-matter SCSS entry compiles to
the EXACT same CSS as main, in both compressed and expanded modes
(12/12 byte-identical). Branch's structural files (v1/v2 partials,
manifests, scripts, hook, .claude/settings.json) are intact.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018Z78wTEczDqpD4nqJWKRME

Files changed

Integration (merge) commit — no direct file changes.