Add server authority, action exchange, routing, usage, and schema preflight

[EricSun0218]

Summary

• add Agent Plugins 1.0 compatibility
• enforce identity-derived session and actor authorization
• add host-controlled audience projection
• add durable engine-neutral action exchange and operation ID v2
• add trusted named model routing
• expose authorized durable usage and explicit known/unknown model costs
• preflight final tool schemas before provider requests

Verification

• local Release build: 0 warnings, 0 errors
• 807 tests passed
• Windows/Linux CI, NuGet consumer, public-tree, Unity package, and Godot 4.7 .NET editor gates passed
• manual branch CI: https://github.com/EricSun0218/OpenGameAgent/actions/runs/31579185230

[EricSun0218]

Superseded by an exact-tree GitHub-signed reconstruction because the main ruleset requires every source commit to be verified.