Reimagine the UI with the "Nocturne" design language

[vssinghh]

A ground-up visual redesign around the idea that Hush is the moment
after the noise stops — hushed, editorial, restrained:

• Typography: serif (system Noto Serif) display/headline/title-large
  styles for an editorial voice; sans for everything read at speed
• Color: light theme becomes warm linen paper with a deep dusk-indigo
  primary; dark theme a near-black midnight sky with moonlit lilac.
  The six candy accents collapse into a dusty semantic set (ember red
  = block, dusk gold = mute, sage = allow; slate/plum/teal metadata)
• Surfaces: flat cards with hairline borders and larger radii replace
  tonal fills and drop shadows; new QuietSurface component
• Navigation: floating pill bottom bar with an expanding filled pill
  for the selected tab, replacing the stock NavigationBar
• Chat: solid ink user bubbles, serif "h" monogram avatar, bordered
  pill input, theme-aware AI status bubbles (drops the light-only
  pastel hacks so dark mode renders correctly)
• Rules: action-colored edge bars, outlined attribute chips
• History: serif italic datelines, serif monogram discs, tint-based
  status badges that work in both themes
• Settings: sections grouped into hairline-bordered islands with
  soft-washed icon tiles
• Onboarding: dusk-gradient hero reserved as the app's one gradient
  moment, serif wordmark and italic tagline

All test tags, user-visible strings relied on by tests, and ViewModel
contracts are unchanged.

Co-Authored-By: Claude Fable 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01N5ZagcBdYgvCwzCpJGRBH1