feat: add savings product recommendation engine

[Joewizy]

Closes #463

Summary

• Add GET /savings/recommendations endpoint returning personalized product suggestions
• Build scoring algorithm that considers: transaction patterns, risk tolerance (derived from withdrawal ratio + product mix), savings
  goals alignment, portfolio diversification, and APY
• Generate human-readable reasons explaining each recommendation
• Project earnings using compound interest based on user's average deposit amount
• Return top 5 recommendations sorted by match score (0-1)

Test plan

• GET /savings/recommendations returns up to 5 scored products
• User with long-term goals gets higher scores for FIXED products
• User with high withdrawal ratio is classified as low risk tolerance
• User with only FLEXIBLE products gets diversification boost for FIXED
• New user with no history gets reasonable default recommendations
• Projected earnings use compound interest formula correctly
• Only active products are recommended

[vercel]

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Project	Deployment	Actions	Updated (UTC)
nestera	Ready	Preview, Comment	Mar 29, 2026 7:22pm

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