[Design P2] Align design tokens: text colors, card border radius, and borders

[AnilChinchawaleXDC]

Source: DESIGN-AUDIT.md

Problem: Text colors don't match spec (#F9FAFB vs #F1F5F9, #9CA3AF vs #94A3B8). Card border-radius is 16px instead of 12px. Card borders use rgba(255,255,255,0.06) instead of border-slate-800/50.

Actions:

1. Update primary text color to #F1F5F9
2. Update secondary text color to #94A3B8
3. Change card border-radius from 16px to 12px
4. Update card borders to border-slate-800/50
5. Document design tokens

Risk: Visual inconsistency, brand dilution.

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Mirrored from Paperclip OPEA-370 (https://agi.openscan.ai/OPEA/issues/OPEA-370)