Last.fm importer keyboard navigation, scrolling, and match clarity

[rianjs]

Track the approved Last.fm importer review pass on feature/43-parallel-lastfm-history-download: keyboard/roving focus behavior, independent native scroll regions, clearer count/track match labels, strong-match advisory rules, and optional IDs for album-level IPC actions. Draft PR #44 implements this work.

[rianjs]

Issue #45: Last.fm count-merge visualization

Outcome

Make an expanded count merge visibly explain how multiple Last.fm source names
and counts resolve onto one Spotify track. Preserve all matching, aggregation,
persistence, and import behavior.

Implementation

• Rework FuzzyPanel using semantic HTML and native CSS grid/flex/borders.
• Show source names and counts, a decorative convergence connector, and the
  resulting count with mode-specific explanatory text.
• Rename Show names / Hide names to Show merge / Hide merge.
• Preserve collapsed-by-default, locked, and session-wide count-mode behavior.
• Keep controls accessible; hide decorative geometry from assistive technology
  and announce the resulting count as normal dynamic status.
• Add no dependency unless native primitives prove inadequate during empirical
  validation; discuss the tradeoff before adding one.
• Avoid Rust, persistence, Spotify API, and architecture changes unless tracing
  reveals an actual contract change.

Evidence

• Extend the existing dependency-free frontend tests for Sum, Use highest, and
  Zero presentation data.
• Run frontend tests, lint, typecheck, and production build.
• Install and validate with Computer Use: expand/collapse, keyboard operation,
  all count modes, locked state, narrow/wide resizing, responsiveness, and no
  Spotify/library side effects. Restore the original count mode afterward.

Delivery

Continue on feature/43-parallel-lastfm-history-download and draft PR #44.
Use one Luna/max implementer and one independent Terra/high TDD reviewer, then
run up to three cr review <pr-url> passes with inline replies. Do not merge
without explicit user authorization.