Implement Holdings Management (Add/Update/Remove Assets)

[grantfox-oss]

Description:
Implement features to add, update, and remove holdings (assets) from portfolios. Include validation for asset symbols, quantities, and cost basis.

Acceptance Criteria:

• Add holding to portfolio (symbol, quantity, cost_basis, chain)
• Update holding (quantity, cost basis rebalancing)
• Remove holding from portfolio
• Validate asset symbol format (3-10 chars)
• Support multiple chains (Ethereum, Polygon, Binance, Solana)
• Update portfolio value calculations on holding change
• Track cost basis for tax calculations
• Prevent duplicate holdings (same symbol + chain)

Definition of Done:

• Holdings can be added/updated/removed
• Portfolio metrics auto-update
• Validation working correctly
• Unit tests > 85% coverage

Test Requirements:

• Unit tests for holding operations
• Integration tests with portfolio updates
• Tax basis calculation tests

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[dorisadams]

I would love to work on this issue, please assign the issues to me so i Can work on it ASAP

[michaelvic123]

I’d love to work on this issue. I’m a full-stack developer with experience building and maintaining web applications across both frontend and backend technologies. The issue looks interesting, and I’m confident I can contribute a solid solution.

[grantfox-oss]

🦊 GrantFox — @michaelvic123 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #31)
2. Your PR will be reviewed by the SourceXXL maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@michaelvic123's PR #43 was approved and merged by @memplethee-lab.

🏆 @michaelvic123: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (688 total points). Track your full progress on GrantFox.

👏 Great work, @michaelvic123! Keep contributing to SourceXXL.