Add trust score calculation examples

[agentmecz]

Document how the composite trust score is calculated with real examples.

What needs to be done:

• Add docs/examples/trust-scores.md
• Show how reputation (50%), stake (30%), and endorsements (20%) combine
• Include example calculations with actual numbers
• Explain trust decay (5% per 14 inactive days)

Resources: Trust module in sdk/src/trust/, contract in contracts/src/TrustRegistry.sol