feat: initial fischer-agentkit package with unified agent architecture
- BaseAgent with handle_task() pattern (execute template moved up)
- Protocol: TaskMessage, TaskResult, HandoffMessage, EvolutionEvent
- Tool system: FunctionTool, AgentTool, ToolRegistry with versioning
- Memory system: WorkingMemory (Redis), EpisodicMemory (pgvector), SemanticMemory (RAG adapter), MemoryRetriever (hybrid)
- Evolution engine: Reflector, PromptOptimizer (DSPy-style), StrategyTuner, ABTester, EvolutionStore
- Orchestrator: PipelineEngine (parallel DAG), PipelineLoader (YAML), HandoffManager, DynamicPipeline
- MCP: Server (FastAPI), Client (httpx), MCPTool
- Prompts: PromptTemplate, PromptSection
- Exceptions: full hierarchy including Tool, Schema, Handoff, Evolution errors
- Tests: unit tests for core, tools, protocol, evolution, pipeline
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