feat: add share-by-URL for search parameters

[Idrhas]

Summary

Closes #6

Encodes the current search inputs (source, destination, amount, direction, and network) as URL query parameters so a user can copy the URL and share it. Opening the URL pre-fills the form and runs the search automatically.

Changes

src/app/page.tsx

• Added useRouter and useSearchParams from next/navigation
• encodeAsset / decodeAsset helpers serialise AssetRef to/from ?src=XLM or ?src=CODE:ISSUER - malformed params return undefined (no crash)
• Bootstrap useEffect fires once after network hydration, reads URL params, and calls search() only when all params are valid
• handleSearch pushes a history entry via router.push() before calling search() so the back button works correctly
• Polling re-fetches go through refresh() and never touch the router

src/components/path-form.tsx

• Added four optional props: initialSource, initialDestination, initialAmount, initialDirection
• All props default to the same values previously hardcoded - fully backwards compatible
• useState initialisers use the URL-seeded values when provided

src/hooks/use-paths.ts

• Added refresh() alongside search() - both share the same internal logic
• refresh() signals to callers (polling) that no history entry should be pushed

Acceptance Criteria

• After a search, the URL contains ?src=&dst=&amount=&dir=&net= params
• Pasting the URL into a new tab pre-fills the form and runs the search automatically
• Malformed query parameters do not crash the app (graceful fallback to defaults)
• The browser back button navigates to the previous search state
• Polling re-fetches do not push a new history entry

[vercel]

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[RaymondAbiola]

@Idrhas please resolve conflicts, thank you.

[RaymondAbiola]

@Idrhas Kindly resolve pr conflicts