docs: 文档清理与重构 — 统一为 3 个核心文档

- 删除 5 个过时/残留文档(project_plan/agent_prompt/optimization_plan/report_db_design/deploy/README)
- 新建 docs/architecture.md(项目架构:11 包职责+数据模型+配置+产物)
- 重写 docs/user-guide.md(CLI 全量+增量/断点续跑+MCP+FAQ)
- 重写 README.md(精简入口+文档索引)
- 更新 continuation.md(追加本次记录)
- 更新 .gitignore(排除 data/* 运行产物)

embedding/__init__.py

@@ -0,0 +1,52 @@
+"""Embedding 向量化模块 (M5)。
+
+公共 API:
+    - EmbeddingResult / EmbeddingError / EmbeddingProviderType
+    - EmbeddingProvider / AsyncEmbeddingProvider (ABC)
+    - compose_text                 (统一文本组装策略)
+    - DashScopeEmbeddingProvider / DashScopeAsyncEmbeddingProvider
+    - LocalBGEEmbeddingProvider / LocalBGEAsyncEmbeddingProvider (可选)
+    - resolve_provider_type / make_sync_provider / make_async_provider
+"""
+
+from .base import (
+    MAX_TEXT_CHARS,
+    AsyncEmbeddingProvider,
+    EmbeddingProvider,
+    compose_text,
+)
+from .factory import (
+    make_async_provider,
+    make_sync_provider,
+    resolve_provider_type,
+)
+from .models import (
+    EmbeddingError,
+    EmbeddingProviderType,
+    EmbeddingResult,
+)
+from .remote import (
+    DASHSCOPE_BATCH_LIMIT,
+    DASHSCOPE_DEFAULT_DIM,
+    DASHSCOPE_DEFAULT_MODEL,
+    DashScopeAsyncEmbeddingProvider,
+    DashScopeEmbeddingProvider,
+)
+
+__all__ = [
+    "DASHSCOPE_BATCH_LIMIT",
+    "DASHSCOPE_DEFAULT_DIM",
+    "DASHSCOPE_DEFAULT_MODEL",
+    "MAX_TEXT_CHARS",
+    "AsyncEmbeddingProvider",
+    "DashScopeAsyncEmbeddingProvider",
+    "DashScopeEmbeddingProvider",
+    "EmbeddingError",
+    "EmbeddingProvider",
+    "EmbeddingProviderType",
+    "EmbeddingResult",
+    "compose_text",
+    "make_async_provider",
+    "make_sync_provider",
+    "resolve_provider_type",
+]