fix: replace wallet-error alert() with Toast in Navbar

[EmeditWeb]

Problem

The Navbar component (lines 156, 223) uses alert() for wallet connection errors. The app has a Toast system (src/components/ui/Toast.tsx) that should be used instead. Browser alert() dialogs are modal, unstyled, and provide a poor UX.

Root Cause

Error handling was added before the toast system existed and was never updated.

What To Build

Replace both alert() calls in Navbar.tsx with addToast({ type: "error", message }) from the toast context.

Files To Touch

• src/components/layout/Navbar.tsx — lines 156, 223 replace alert() with addToast()

Acceptance Criteria

• No alert() calls remain in Navbar.tsx
• Wallet connection errors shown as styled toast notifications
• Toast auto-dismisses after 5 seconds

Mandatory Checks

• context/ files read
• npm run build passes
• PR references this issue