P1: host-agnostic quercus-core with agent loop, providers, and tool schemas

- Core types: Rational time, EntityId, ActionBatch, PngBytes (no Pillow dep)
- Config: ~/.quercus/config.toml with 0600 perms, env var override for CI
- LLMProvider: Claude (anthropic SDK) and OpenAI-compatible endpoint
  (covers custom gateways and llama.cpp server mode); graceful degradation
  without API keys
- Tool schemas: 26 curated tools with JSON Schema and read_only flags
- AgentLoop: sync dialogue loop with confirmation gate (read-only batches
  bypass, rejected mutations are reported back to the LLM), PNG frame
  feedback for multimodal providers
- Session log: JSONL recording with frame sha256 hashes, replayable
- HostAdapter ABC (signatures only, aligned with OPP/1 method families)
- Mock LLM provider (scripted/replay/record) for network-free CI

Tests: 69 passed via uv run pytest (no network access)

tests/conftest.py

@@ -0,0 +1,25 @@
+"""pytest 全局配置：把 tests/ 加入 sys.path（供 ``import mock_llm``）与共享 fixtures。"""
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+import pytest
+
+_TESTS_DIR = Path(__file__).resolve().parent
+if str(_TESTS_DIR) not in sys.path:
+    sys.path.insert(0, str(_TESTS_DIR))
+
+
+@pytest.fixture
+def tmp_home(tmp_path, monkeypatch):
+    """把 ~/.quercus 定向到临时目录（经 QUERCUS_HOME 覆盖）。"""
+    home = tmp_path / "home"
+    monkeypatch.setenv("QUERCUS_HOME", str(home))
+    return home
+
+
+@pytest.fixture
+def fake_png():
+    """最小 PNG 头 + 填充字节；core 只流转字节，不解码。"""
+    return b"\x89PNG\r\n\x1a\n" + bytes(range(64))