feat(ui): polish home design — branded header, emphasized scan v1.092

First pass of the broader visual polish the user asked for.

- Refined color tokens (slightly deeper brand green, added brand_soft,
  danger, scrim) for a more modern, cohesive palette.
- Home header: brand mark (scan glyph in a gradient brand circle) + name
  in on-surface, version shown as a soft brand chip.
- Action card: Scan is now the primary action (filled gradient circle,
  white glyph, bold label); Import/ID use the soft container with
  brand-tinted glyphs — clear visual hierarchy.
- "Recent" section label restyled as a quiet uppercase-style caption.
- List rows: larger rounded thumbnail with brand-soft placeholder, 18dp
  card radius.

Constraint: ViewBinding ids (title, versionText, actionScan/Import/Id, list, empty, selection*) preserved.
Confidence: high
Scope-risk: local
Reversibility: trivial
Directive: next — live filter-preview thumbnails in the editor and per-page progress in batch processing (per user reference shots).
Tested: assembleDebug + testDebugUnitTest exit=0.
Not-tested: on-device visual look.
Related: design polish pass 1

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