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/core/test_host_adapter.py

@@ -0,0 +1,72 @@
+"""HostAdapter ABC：只定义接口形状，不可实例化，方法签名齐全。"""
+import pytest
+
+from quercus_core.host.adapter import HostAdapter
+from quercus_core.types import Action, ActionBatch, Limits, Rational
+
+
+def test_abc_cannot_instantiate():
+    with pytest.raises(TypeError):
+        HostAdapter()  # type: ignore[abstract]
+
+
+def test_abstract_methods_declared():
+    assert {"capabilities", "limits", "get_frame", "get_thumbnails", "execute", "undo_last"} <= set(
+        HostAdapter.__abstractmethods__
+    )
+
+
+def test_missing_abstract_method_raises():
+    class Partial(HostAdapter):
+        def capabilities(self):
+            return set()
+
+    with pytest.raises(TypeError):
+        Partial()  # type: ignore[abstract]
+
+
+def test_concrete_subclass_works():
+    class Impl(HostAdapter):
+        def capabilities(self):
+            return set()
+
+        def limits(self):
+            return Limits()
+
+        def open_project(self, path): ...
+
+        def save_project(self, path=None): ...
+
+        def get_project_overview(self): ...
+
+        def probe_media(self, path): ...
+
+        def import_footage(self, paths): ...
+
+        def get_timeline_structure(self, seq): ...
+
+        def get_frame(self, target, time, max_size): ...
+
+        def get_thumbnails(self, target, range, count): ...
+
+        def get_audio_levels(self, seq, range, resolution): ...
+
+        def play(self, speed=1.0): ...
+
+        def pause(self): ...
+
+        def seek(self, time): ...
+
+        def get_state(self): ...
+
+        def export(self, seq, output, preset): ...
+
+        def execute(self, batch): ...
+
+        def undo_last(self): ...
+
+    impl = Impl()
+    assert impl.capabilities() == set()
+    assert impl.limits().max_frame_rate == 8.0
+    # execute 接受 ActionBatch 语义
+    impl.execute(ActionBatch(label="t", actions=[Action(tool="play", params={})]))