paraglide: variants for bucket labels + empty-state + chip ARIA

[electather]

Part of epic #491. PRD US-011. Review comments on:

• bucket-chips.tsx:15
• empty.tsx:46
• all-items/index.tsx:57
• sort-select.tsx:12
• lib/types.ts:41

Owner direction: "use paraglide variants for this" repeated across 5+ sites.

Goal

Bucket labels, empty-state copy, bucket-chip ARIA labels expressed as Paraglide variants keyed on {bucket} — one message instead of five near-identical entries per locale.

Acceptance criteria

• messages/<locale>.json exposes variants:
  • watchlist_bucket_label({bucket})
  • watchlist_empty_title({bucket})
  • watchlist_empty_body({bucket})
  • watchlist_bucket_chip_aria({bucket})
• * selector (or explicit default) handles unknown values without crash.
• Old per-bucket flat messages deleted — no compat shims.
• Paraglide generated message imports drive bucket chip + empty state copy — no string literals in components.
• bucket-chips.tsx:84 chip count suggestion applied: <span className="font-mono text-xs tabular-nums opacity-70">{count}</span>.
• Verify in browser: each bucket shows right copy; locale switch reflects immediately.

Reference

Use paraglide-js skill on first variant authoring. Match existing positional vs named match form in repo.