feat: compact tag cloud spiral with controlled overlap

feat: compact tag cloud spiral with controlled overlap

Tighten tag cloud spacing by adjusting spiral parameters:
- padding: 8 → -2 (allows ~2px edge overlap, ~7-10% of tag height)
- aStep: 0.3 → 0.2 (finer angular sampling per revolution)
- rScale: 0.018 → 0.013 multiplier (28% tighter spiral arms)
- attempt cap: 2000 → 3000 (compensate for smaller aStep)

Tags now cluster closer together visually while remaining readable.
Narrow viewport fallback (< 400px) and 404/sidebar placements unaffected.

Co-Authored-By: Claude Haiku 4.5 <redacted>