Fix vault returns and grouping UI

[miohtama]

Why

The vault pages need clearer returns and grouping behaviour: gross/net return cells should show annualised headline metrics while still exposing raw sampled-period returns, and vault grouping pages need more robust stablecoin, protocol, and market-share metadata handling.

Lessons learnt

• Short-period returns are easy to misread when raw and annualised values are mixed in the same table, so the UI needs explicit tooltip labelling for both values and the sampled date range.
• Stablecoin and protocol metadata helpers need to gracefully handle unknown or off-chain denominations so grouped vault pages do not produce broken links or misleading labels.

Summary

• Annualise the gross/net values in the vault returns and fees table, with per-cell tooltips for annualised value, raw value, and sampled period.
• Improve fee-adjusted vault metric messaging, stablecoin denomination links/logos, and grouped vault table/filter behaviour.
• Add supporting helper coverage and static flag/logo assets used by the updated vault grouping UI.