feat: persist Freighter sessions

[kaycke1337]

Summary

• restore allowed Freighter sessions on load without prompting again
• persist and synchronize the preferred Stellar network across tabs
• watch Freighter address/network changes and clear cached Stellar stealth keys when wallet state changes
• add install/approve CTA states with 30s retry polling after opening the Freighter install page

No wallet signatures or sensitive key material are cached; Stellar stealth keys are cleared on disconnect, address changes, and network changes.

Closes #4

Validation

• npx prettier --check .
• npx tsc --noEmit
• git diff --check
• npx vite build
• npx pnpm@10 build

Build completed successfully. Vite still reports existing dependency/chunk-size warnings from bundled wallet SDK dependencies.

[vercel]

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[truthixify]

The Freighter session persistence work in StellarWalletContext.tsx and WalletConnect.tsx is what #4 asked for: isConnected/isAllowed restoration, network change listener, install detection, BroadcastChannel cross-tab sync.

GitHub marks the PR mergeable, but a local test merge shows your branch (off pre-develop main) would silently revert the sponsored-withdrawal hooks from #29 in StellarReceive.tsx (the feeBumpHash, showSponsorPrompt state your diff removes was just added). Rebase needed:

git fetch origin
git rebase origin/develop
git push --force-with-lease

Keep your context changes; drop the StellarReceive.tsx and StellarSend.tsx reverts during the rebase (they were stale-base artifacts, not intentional). Thanks @kaycke1337.