feat(ui): premium pass 1 — elevated cards, richer filter strip, framed viewer v1.103

User asked to make the app look more substantial / less amateurish across
filters, UI, and the viewer.

- Cards now float with shadow elevation instead of flat 1px strokes: home
  action card (4dp), recent-scan rows (2dp), result / OCR cards (3dp),
  group grid thumbnails. Gives depth and a more premium feel.
- Editor filter strip: larger preview thumbnails (64x82, 13dp radius),
  thicker brand selection ring, and the selected label goes bold + brand
  colored — the active filter reads clearly.
- Viewer (CamItemActivity): the page pager now sits inside a rounded
  elevated surface card, so scanned pages look framed rather than raw.
- Added shadow / bar-surface color tokens for consistency.

Constraint: ViewBinding ids unchanged; CamGalleryAdapter still casts the gallery item root to ImageView so that layout root was left intact.
Confidence: high (builds clean) / medium (visual polish needs on-device confirmation)
Scope-risk: local (layout/visual only)
Reversibility: trivial
Directive: this is pass 1; iterate on camera chrome, bottom toolbars, and typography once on-device screenshots show what still reads as plain.
Tested: assembleDebug + testDebugUnitTest exit=0 (22 tests).
Not-tested: on-device rendering of elevations and the framed viewer.
Related: v1.092 home polish

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