docs(integrations): add Phoenix DEX multi-hop swap + stealth announce guide

[sanusishafii989]

Summary

Closes #125

Adds the Phoenix DEX integration guide, completing the DEX documentation suite alongside Soroswap and Aquarius. The guide covers quoting multi-hop routes via the on-chain Phoenix Router, slippage/deadline parameter construction, and wrapping a swap + stealth-announce in a single fee-bumped transaction.

Changes

• New file: guides/integrations/phoenix.mdx
  • Overview & features with a comparison callout (Phoenix vs. Soroswap: routing model, dynamic multi-hop, fee tiers, PHO incentives)
  • Multi-hop route quoting via Soroban simulateTransaction (XLM → PHO → USDC)
  • Slippage (min_amount_out) and deadline parameter construction
  • Combined atomic transaction: Phoenix swap + Wraith announce in a single tx
  • Fee-bump wrapping via TransactionBuilder.buildFeeBumpTransaction
  • Complete Futurenet end-to-end runnable example
  • Recipient scanning, error handling with retries, production checklist
• Modified: guides/integrations/_meta.json — registered phoenix (and other existing integration pages that were missing)
• Modified: docs.json — added guides/integrations/phoenix to the Integrations nav group; consolidated duplicate Integrations groups into one
• Modified: guides/integrations/soroswap.mdx — added cross-link to phoenix.mdx in the "See also" section

Acceptance Checklist

• guides/integrations/phoenix.mdx exists with all required sections
• All 9 TypeScript code snippets pass compilation (tsc --noEmit with the same ambient prelude as CI check:snippets)
• Runnable Futurenet end-to-end example included (XLM → USDC via Phoenix router → stealth announcement)
• Navigation sidebar includes "Phoenix DEX" in both _meta.json and docs.json
• Cross-linked bidirectionally with guides/integrations/soroswap.mdx
• Fee-bumped transaction wrapping documented (TransactionBuilder.buildFeeBumpTransaction)
• Differences vs. Soroswap callout included (routing model, multi-hop, fee tiers)

Closes #125

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[truthixify]

Thanks @sanusishafii989. Only docs.json conflicts here. #135 rewrote the nav and two more guides landed after it, so your Integrations entry needs re-adding on top:

git fetch origin
git rebase origin/develop

guides/integrations/phoenix.mdx itself is untouched by the conflict, and the Soroswap cross-link is a nice touch.