Add Stable Hub bridge callout

[probablyangg]

Summary

• Add a prominent Stable Hub callout near the top of the bridge reference page.
• Direct mainnet users to the first-party bridge entry point.
• Preserve clear paths for integration builders and developers using the TypeScript testnet tutorial.

Why

The bridge page opens with a technical provider comparison, but users who only want to move funds to Stable do not get a prominent next action. The existing testnet tutorial link is also easy to miss and serves a different, developer-focused use case.

Impact

Mainnet users can go directly to Stable Hub, while integration builders and testnet developers retain their existing technical paths.

Validation

• npm run check

[github-actions]

Styleguide check

✓ 132 en pages — 0 blocking, 11 warnings

docs/pages/en/explanation/autobahn.mdx

• ⚠ warning: marketing word "robust" (L20)
• ⚠ warning: marketing word "seamless" (L34)

docs/pages/en/explanation/consensus.mdx

• ⚠ warning: marketing word "robust" (L32)

docs/pages/en/explanation/ethereum-compatibility.mdx

• ⚠ warning: marketing word "seamless" (L10)

docs/pages/en/how-to/monitor-node.mdx

• ⚠ warning: marketing word "comprehensive" (L7)

docs/pages/en/how-to/troubleshoot-node.mdx

• ⚠ warning: marketing word "comprehensive" (L7)

docs/pages/en/reference/indexers.mdx

• ⚠ warning: marketing word "seamlessly" (L9)

docs/pages/en/reference/ramps.mdx

• ⚠ warning: marketing word "seamless" (L28)

docs/pages/en/reference/system-transactions-api.mdx

• ⚠ warning: marketing word "comprehensive" (L358)

docs/pages/en/reference/wallets.mdx

• ⚠ warning: marketing word "powerful" (L83)
• ⚠ warning: marketing word "seamless" (L30)

_{Enforced by npm run style:check — see STYLEGUIDE.md.}