fix: address code-review findings from pass 1 + 2 (#8)

- Fix saveCourseToDB returning 0 on conflict by falling back to SELECT
- Fix inactive layouts showing 'Never played' when last_played exists
- Add .icon-btn.spinning to courses.css for refresh button feedback
- Remove duplicate .btn-primary from courses.css (use shared.css version)
- Tokenize rating tier colors into --rating-tier-{high,mid,low} CSS vars
- Convert var to const/let throughout courses.js
- Fix logger.error calls to use {err} object form (pino convention)
- Extract RATING_TIER_HIGH/MID constants in course-layouts.ejs scriptlet
- Remove dead href='#' View all link from courses.ejs (deferred)
- Pass total prop explicitly from course-table.ejs to course-cards.ejs
- Remove dead #search-results-info selector from mobile.css
- Remove redundant .replace(/"/g, '"') from data attributes in course-table.ejs

public/css/mobile.css

@@ -64,9 +64,6 @@
         display: none;
     }
 
-    /* Hide search result info text on courses (mobile has section-head) */
-    #search-results-info { display: none; }
-
     /* ── Container ──────────────────────────────────── */
 
     .container {