Initial commit: Lush vs Bash AI benchmarking framework

Benchmark harness that uses LLM agents to solve shell scripting tasks
in both Bash and Lush, then compares correctness and code quality.

- CLI with run, run-all, list-tasks, report, and export commands
- Agent loop with retry support via Anthropic Claude provider
- Test harness executing solutions in sandboxed subprocesses
- LLM-driven questionnaire for subjective code quality evaluation
- HTML report export with charts (matplotlib)
- 8 Category A tasks (write-from-scratch in both languages)
- 4 Category B tasks (verify provided Bash, convert to Lush)
- Lush language reference for agent context

lush_bench/providers/base.py

@@ -0,0 +1,17 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Protocol
+
+
+@dataclass
+class Message:
+    role: str  # "user" or "assistant"
+    content: str
+
+
+class LLMProvider(Protocol):
+    def send(self, messages: list[Message], system: str = "") -> str: ...
+
+    @property
+    def model_name(self) -> str: ...