feat(stellar): add expert deep links

[Hallab7]

Stellar Expert deep-link helper everywhere

Summary

• add network-aware Stellar Expert URL helpers for accounts, transactions, and contracts
• add a reusable StellarLink component with an adjacent copy affordance
• make Stellar addresses and transaction hashes clickable across wallet, send, receive, vault, split, and activity views
• add activity and debug routes with clickable transaction hashes, wallet addresses, and deployed contract IDs
• retain the existing explorer helper exports as compatibility wrappers

Testing

• pnpm exec vitest run src/utils/stellarExpert.test.ts
• pnpm exec tsc --noEmit
• pnpm run build
• verified a repository grep for hardcoded explorer-domain URLs returns zero results

Acceptance criteria

• No hardcoded Stellar Expert URLs remain
• Every activity row's transaction hash links to the active network
• The wallet picker's connected Stellar address is clickable
• Contract IDs in the debug panel are clickable
• Every Stellar link includes a copy affordance

closes #101

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[truthixify]

Rebase after the recent merges. Your three demo PRs conflict against develop now.

[truthixify]

Same cascade situation as #140, rebase against develop.

[truthixify]

Sorry, dirtied again — I removed the Playwright block from ci.yml on develop and it clashed with your base. Rebase against latest develop and force-push, that should be the last conflict for a while.

[truthixify]

Merged. Solid deep-link integration @Hallab7. The expert.host routing logic is well-factored.