feat: add unsaved changes confirmation to settings page (Closes #1086)

[sojetunde8]

Closes #1086

Summary

• Track dirty state by comparing initial vs current values for all editable settings fields
• Add native beforeunload handler to warn on tab close, browser refresh, and back/forward navigation
• Add window.confirm prompts for in-app navigation via the "Connect Wallet" button and "Disconnect Wallet" button when dirty
• Replace the "Connect Wallet" <Link> with a <button> to intercept navigation with confirmation

Testing

• Added 7 unit tests covering: clean start, dirty detection for each field (theme, currency, format, decimals), no-confirm when unchanged, and disconnect flow without changes

[ogazboiz]

good instinct on #1086 and the test coverage is appreciated, but two design problems block this:

1. settings on main persist immediately (toggleTheme writes localStorage on click), yet isDirty stays true forever after any change, so users get warned about "unsaved" changes that are already saved. either introduce a real draft-plus-save model or reset initialValuesRef after each apply.
2. the guard only wraps the two in-page buttons. all navbar links and any other internal Link navigation bypass it entirely, so the stated goal is not met. cover app-internal navigation or scope the issue down explicitly.
3. small ones: the Link to button swap loses link semantics, and there is a stray blank-line diff where handleDisconnect was touched.

if you want to keep contributing, join us on Telegram: https://t.me/+DOylgFv1jyJlNzM0

[sojetunde8]

good instinct on #1086 and the test coverage is appreciated, but two design problems block this:

1. settings on main persist immediately (toggleTheme writes localStorage on click), yet isDirty stays true forever after any change, so users get warned about "unsaved" changes that are already saved. either introduce a real draft-plus-save model or reset initialValuesRef after each apply.
2. the guard only wraps the two in-page buttons. all navbar links and any other internal Link navigation bypass it entirely, so the stated goal is not met. cover app-internal navigation or scope the issue down explicitly.
3. small ones: the Link to button swap loses link semantics, and there is a stray blank-line diff where handleDisconnect was touched.

if you want to keep contributing, join us on Telegram: https://t.me/+DOylgFv1jyJlNzM0

Rsolved, @ogazboiz