docs: Add security requirements section for third-party bridges

[S0nee]

Motivation: Users often lack adequate understanding of third-party bridge security risks. Many incorrectly attribute responsibility for bridge-related incidents to the ecosystem team rather than the bridge operators, creating confusion about liability boundaries.

Solution: Add a structured description of the key risks of using third-party bridges. Also supplement this with a description that clearly delineates the responsibilities between the bridge teams and the Abstract team.

[cursor]

PR Summary

Docs update: Third-party bridge security

• Adds a Warning section in tooling/bridges.mdx under "Third-party Bridges" outlining smart contract, operational, and liquidity risks.
• Clarifies liability by stating the Abstract team is not responsible for third-party bridge issues.
• Documentation-only change; no code or behavior modifications.

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