Switch colour palette to deep forest green

[rastermanden]

Summary

• Replaces the warm terracotta accent (#c96442) with a rich moss/forest green (#2d7a4f)
• Shifts header background to a near-black forest tint (#0e1a13)
• Tints all surfaces (cream, ivory, sand, borders) with a faint green hue
• Muted text colours shift to warm sage greens

Test plan

• Check header, buttons, and FAB render in forest green
• Check gem markers on map use the new accent colour
• Check empty state, modal, and form borders look consistent
• Check selected gem card left-border accent

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