feat: redesign homepage tiles — post inner frames, list manifests, grid layout

- Header is now a 1-col 2-row vertical nameplate tile
- Post tiles have inner frame borders, scanline texture, and
  padding variation (tile-airy) for visual rhythm
- List tiles are visually distinct: dashed borders, extracted
  item previews with › bullets, +N more counters
- Log tile is 2x3, placed early in the grid with scrollable entries
- Everything lives inside the mosaic grid — no non-grid content
- Smarter sizing: posts mostly 1x1, lists always 2-wide,
  shots varied by image count and position