Add v3.0.0 core modules for agents and prompts

[a6b8]

Summary

• Add IdResolver (parse, resolve, validate ID schema)
• Add AgentManifestLoader (load manifests and prompts)
• Add AgentManifestValidator (AGT001-AGT012 rules)
• Add AgentTestRunner (tool/content comparison)
• Add PromptLoader (Provider + Agent prompt validation)
• Add TST001 test minimum enforcement in MainValidator
• Add Pipeline.loadAgent() method
• Export 5 new classes, add 3 new FlowMCP methods (total: 20 exports, 15 methods)

Files

• 5 new: IdResolver, AgentManifestLoader, AgentManifestValidator, AgentTestRunner, PromptLoader
• 3 modified: index.mjs, MainValidator.mjs, Pipeline.mjs
• Updated test fixtures for v3 test minimum compliance