Add targeted annual return calculation and display for assets

[Copilot]

Adds targeted annual return percentage display for assets based on standard finance formula combining risk-free rate, equity risk premium, and expected growth.

Changes

Database

• Added risk_free_rate, risk_premium, expected_growth_rate decimal fields to assets table

Backend

• Asset#targeted_annual_return calculates return as sum of three rate components
• Exposed via JSON serialization

Frontend

• AssetCard shows return percentage in card details
• Asset detail page displays return with explanatory context

Example

asset = Asset.create(
  risk_free_rate: 4.5,      # T-bill baseline
  risk_premium: 8.0,         # Equity risk
  expected_growth_rate: 15.0 # Growth projection
)

asset.targeted_annual_return # => 27.5

Seeds updated with realistic values. Unit tests cover calculation edge cases.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>display a targeted annual return (percentage) for each asset</issue_title>
<issue_description>the targeted annual return should be based on a real formula using estimated real-world parameters. add fields to the asset model as required by the formula</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes display a targeted annual return (percentage) for each asset #27

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