Feat: Fuse -> Celo staking migration: modal on Savings and Stake

[blueogin]

Is your feature request related to a problem? Please describe.

Users with G$ staked on Fuse (GovernanceStakingV2) need to move to Celo Savings. There is no in-app prompt on Savings or Stake when a wallet still has a Fuse governance stake, so migration is easy to miss.

Describe the solution you'd like

On both Savings (/savings) and Stake (/stakes, including GoodDAO Staking and embedded Savings section), detect non-zero stake on old Fuse governance staking and open migration modal immediately.

Desired behavior

• If old Fuse governance stake > 0:
  • Open migration modal automatically on page load (or once data is loaded)
  • No popover/button click required
• If stake = 0:
  • Do not show migration modal
• If wallet disconnects:
  • Close/reset migration modal state

UX notes

• Keep modal as the main flow container (summary → approve/sign → backend migration status/success)
• Keep “not now” / close action in modal
• Avoid repeatedly reopening in same session after user dismisses (unless they re-open manually or refresh behavior is specified)

Acceptance criteria

• On /savings, modal auto-opens when old Fuse stake is detected
• On /stakes, modal auto-opens when old Fuse stake is detected
• No popover is shown for this flow
• Modal does not open when stake is zero
• Modal state resets correctly on wallet change/disconnect
• Existing Savings/Stake flows are not regressed
• i18n and analytics updated for auto-open behavior (e.g. migration_modal_auto_opened)

Describe alternatives you've considered

• Popover + CTA before modal: rejected (extra click, easier to ignore)
• Separate full migration page: rejected as primary UX (modal is faster and contextual)

Additional context

[copilot-swe-agent]

The agent encountered an error and was unable to start working on this issue: Please try again later, or contact support if the problem persists. (Request id: 8386:BA627:61C1CC:7D625A:6A1479DA)