feat: implement pdf report generation

[Stanley-Owoh]

Summary

Completes the PDF report generation logic for GET /api/plans/{id}/report. The report now includes dedicated Assets, Yield Details, and Beneficiaries sections with real-time projected yield computation.

Changes

backend/src/pdf.rs

• Added projected_accrued_yield field to PlanReportData
• Restructured the report into four clear sections:
  • Plan Details — plan ID, owner, status, grace period, created date
  • Assets — token address and locked amount
  • Yield Details — earn yield flag, yield rate (bps + APY%), snapshotted accrued yield, and real-time projected yield
  • Beneficiaries — wallet address, allocation (bps + %), fiat anchor info
• Moved token_address and amount from Plan Details into the new Assets section
• Moved yield fields from Plan Details into the new Yield Details section

backend/src/api.rs

• Added compute_projected_accrued_yield(&plan) call before building the PDF data to calculate real-time accrued yield since the last ping
• Passes the projected yield as projected_accrued_yield into PlanReportData
• Renumbered handler step comments for clarity

Testing

• cargo check passes with no warnings
• PDF generation runs on a blocking thread via tokio::task::spawn_blocking as before

Closes #941

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[ONEONUORA]

@Stanley-Owoh
Run cargo fmt --all -- --check and clippy

[ONEONUORA]

@Stanley-Owoh
Update on this PR

[Stanley-Owoh]

@ONEONUORA Good day maintainer, please review my pr, All checks has passed. Thank you

[ONEONUORA]

Great job @Stanley-Owoh