Issue 38/stellar wallet integration

[Fayedamz]

closes #38

Adds docs/guides/stellar-wallet-integration.mdx.

• Per-wallet quick-start for Freighter, Albedo, xBull, and LOBSTR
• Comparison table: Soroban auth, fee-bump signing, mobile support
• Wallet picker UI pattern with availability detection and React hook
• Stellar Wallets Kit as a one-package alternative
• WalletConnect v2 reference pattern (coming soon)
• Session persistence with localStorage + re-verification
• Mobile detection, wallet matrix, and deep link fallback
• Added to Guides nav in docs.json

Fix: replaced emoji in MDX tables with plain text for Mintlify compatibility.

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[truthixify]

Other docs PRs are landing one by one, which means most of them now conflict on docs.json (because each registers its new page there) and sometimes guides/privacy-best-practices.mdx. Quick rebase clears it:

git fetch origin
git rebase origin/develop
# in docs.json: keep all entries from both sides
# in privacy-best-practices.mdx: keep both your addition and develop's
git push --force-with-lease

Content of the PR itself is clean — this is just the registration ordering.