refactor(scss): drop dead selectors and modernize .tag-input

[alphatownsman]

Summary

Removes ~866 lines of unreferenced SCSS accumulated in the legacy partials, with no behavior change for anything currently rendered. Every class that remains is used by a live template or JS file (verified via grep across **/*.html and **/*.js).

• _legacy.sass (981 → 170): trim dead blocks (entity-list, entity-detail, entity-desc/marks/reviews, review-head, related-user-list, action-panel, mark-panel, review-panel, user-profile, user-relation, report-panel, import-panel, relation-dropdown, track-carousel, aside-section-wrapper, add-entity-entries, dividing-line, tag-collection), unused vars and clear mixin. Keep entity-card, entity-sort(-control), main-section-wrapper, img.emoji.
• _legacy2.scss: drop unused input:invalid#position. #modal, .modal-*, .add-to-list-modal__*, .donut/.hole, .gg-play-button-o are live and kept.
• _dialog.scss: remove @keyframes fadeIn/fadeOut/zoomIn/zoomOut that were illegally nested inside dialog { }; identical top-level keyframes in _legacy2.scss cover both #modal and <dialog> usages.
• _mark.scss: swap hard-coded #ccc, #d5d5d5, #00a1cc, #606c76 in .tag-input* for Pico tokens (--pico-muted-border-color, --pico-muted-color, --pico-primary); drop redundant -webkit-box/-ms-flexbox/-webkit-transition prefixes.
• _common.scss: drop .post span.invisible (redundant with the broader span.invisible rule).

No file deletions, no import changes. All 22 partials in neodb.scss still compile.

Test plan

• uv run pre-commit run -a clean
• manage.py compilescss produces neodb.css without errors
• Manual: .tag-input chips render correctly in both light and dark mode
• Manual: add-to-collection and share-collection modals still animate in/out
• Manual: profile/discover sort-shelves still drag, reorder, and hide
• Manual: podcast play-button icon (.gg-play-button-o) still renders

[gemini-code-assist]

Code Review

This pull request performs a significant cleanup of legacy SCSS and Sass files, removing unused styles, keyframes, and variables while modernizing code by replacing hardcoded colors with CSS variables and removing obsolete vendor prefixes. Feedback focuses on _legacy.sass, specifically regarding the incorrect ordering of max-width media queries—which necessitated the use of !important—and a discrepancy between the documentation and the actual value assigned to the $large-devices breakpoint.

[gemini-code-assist]

When using max-width media queries, they should be ordered from largest to smallest. Currently, the smaller breakpoint ($small-devices) is defined before the larger one ($large-devices), which causes the latter to override the former for small devices. This necessitated the use of !important to force the small-screen styles. Swapping the order allows for a cleaner cascade and removes the need for !important.

[gemini-code-assist]

The comment for $large-devices mentions '992px and up', but the variable is set to 767.98px. This is inconsistent and misleading. The comment should be updated to reflect the actual value used in the code.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.86%. Comparing base (d5f57ae) to head (fe38c2e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1466      +/-   ##
==========================================
- Coverage   60.86%   60.86%   -0.01%     
==========================================
  Files         268      268              
  Lines       26450    26450              
  Branches     3925     3925              
==========================================
- Hits        16100    16098       -2     
- Misses       9016     9018       +2     
  Partials     1334     1334              

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