v0.6.0 — Prompt styles, query preprocess, MCP response_style

RAG prompt variants (thorough/concise), query preprocessing for retrieval, MCP query tool response_style parameter, and evaluator uses config.

RAG & prompts

• Response styles — Two system prompts: thorough (detailed) and concise. Configurable via `ORACLE_RAG_RESPONSE_STYLE` (thorough | concise). Both include a short chain-of-thought instruction.
• Query preprocessing — Normalize whitespace and strip common MCP boilerplate before retrieval; original query still used in the prompt. New `query_preprocess` module and tests.

MCP

• query_tool response_style — MCP query tool accepts `response_style` (string, default thorough). Wrapper preserves function signature so the tool schema lists all parameters.
• Error handling — `_log_tool_errors` decorator preserves `signature` for FastMCP schema introspection.

Evaluation

• Target — `oracle_rag_target` uses `get_response_style()` so runs respect `ORACLE_RAG_RESPONSE_STYLE`.
• run_evaluation — Loads `.env` from cwd or parent before running.

Configuration & docs

• Config — `get_response_style()`; documented in `.env.example` and README.
• Checklist — Prompt engineering iteration updated; pairwise experiments moved to Phase 6.
• Evaluation strategy — How to compare response styles and use env/prefixes.