[contracts] Add Slither and static-analysis plan for v0 contracts

[FlowmemoryAI]

Objective

Add a lightweight static-analysis plan for the v0 contracts foundation, including whether Slither should run locally, in CI, or both.

Context

The current foundation has Foundry tests but no static-analysis gate. Slither or equivalent checks should be evaluated before calling the contracts foundation audit-ready.

Scope

• Evaluate Slither setup and dependency impact.
• Decide whether CI should run static analysis now or later.
• Avoid production deployment config, RPC secrets, or network setup.

Acceptance Criteria

• Recommended static-analysis workflow is documented.
• If CI is added, it is lightweight and does not require secrets.

[FlowmemoryAI]

Live V0 local check: Slither was not available in PATH on this runner.

Documented candidate command in docs/SECURITY_MODEL.md:

slither . --filter-paths tests|script

Keep this issue open for deciding install method and CI scope.