feat(ui): standardize LNB sizing and active depth effect

- Adopt the official LNB desktop spec as package defaults: 240px column,
  14px menu text, 48px 1-depth rows and 42px 2/3-depth rows, with new
  item/subitem padding-block and profile min-height tokens.
- Match --hm-lnb-current-depth to the Storybook Manager selected item:
  sampled soft inset falloff (left/top/bottom) and a fade over the last
  quarter, keeping the concave corners and content join.
- Drop the size overrides from the LNB Story CSS and update the LNB, GNB
  and Dashboard docs, AI guides and the theme verification baseline.

packages/ui/ai/DESIGN_RULES.md

@@ -68,6 +68,7 @@ Brown·Orange 계열 팔레트(`--hm-sem-palette-brown-*`, `--hm-sem-palette-ora
 | Select Trigger 높이 | medium 34 · large 44(기본) | — |
 | Control radius | 4px | `--hm-radius-control-md` → `--hm-radius-button`, `--hm-radius-input`, `--hm-radius-select`, `--hm-radius-container` |
 | Card | border 1px, padding 24px, radius 4px, 그림자 없음 | `--hm-card-*` |
+| LNB(Desktop) | 열 240px, 메뉴 14/28/700, 1뎁스 행 48 · 2·3뎁스 행 42, Profile 48, 콘텐츠 접점 18. 모바일 Header 56 · 링크 44 | `--hm-lnb-width`, `--hm-lnb-item-*`, `--hm-lnb-subitem-*`, `--hm-lnb-third-*`, `--hm-lnb-profile-min-height`, `--hm-lnb-join` |
 | Dialog | radius 8px, padding 24px, Header 아래 16px, Footer 위 16px, 버튼 간격 8px, 그림자 `0 0 12px` 검정 20% | `--hm-dialog-*` |
 
 ## 5. 상태