feat(agents): Scope B A1 — 4 竞品生成器 schema/spec + 2 上下文 builder

续写/扩写/降AI率/拆书 4 个生成器的声明（preview-only writes=[]，只声明 tier #2）：
- schemas.py: ContinuationResult/PolishResult/DeAiResult/BookTeardownResult
- specs.py: continue(writer)/expand(writer)/de-ai(analyst)/teardown(analyst)，各配 system_prompt
- generation_node.py: build_continuation_context(续写读前文)/build_text_input_context(原文输入)
- 单测: 4 spec/schema 契约 + 2 builder 纯函数（确定性/空值降级）

守不变量 #2(只声明 tier)/#3(纯预览不写库)/#9(system_prompt 进缓存前缀)。

packages/agents/ww_agents/__init__.py

@@ -8,12 +8,15 @@ from __future__ import annotations
 from .schemas import (
     Blurb,
     BlurbResult,
+    BookTeardownResult,
     CharacterCard,
     CharacterGenResult,
     CharacterRelation,
     Conflict,
     ConflictType,
+    ContinuationResult,
     ContinuityReview,
+    DeAiResult,
     DetailedOutlineResult,
     ForeshadowReview,
     ForeshadowSuggestion,
@@ -32,6 +35,7 @@ from .schemas import (
     OutlineResult,
     PaceIssue,
     PaceReview,
+    PolishResult,
     Scene,
     StyleDimension,
     StyleDriftReview,
@@ -48,7 +52,10 @@ from .specs import (
     book_title_spec,
     brainstorm_spec,
     character_gen_spec,
+    continue_spec,
     continuity_spec,
+    de_ai_spec,
+    expand_spec,
     fine_outline_spec,
     foreshadow_spec,
     glossary_spec,
@@ -60,6 +67,7 @@ from .specs import (
     refiner_spec,
     style_drift_spec,
     style_extract_spec,
+    teardown_spec,
     worldbuilder_spec,
 )
 
@@ -67,12 +75,15 @@ __all__ = [
     "AgentSpec",
     "Blurb",
     "BlurbResult",
+    "BookTeardownResult",
     "CharacterCard",
     "CharacterGenResult",
     "CharacterRelation",
     "Conflict",
     "ConflictType",
+    "ContinuationResult",
     "ContinuityReview",
+    "DeAiResult",
     "DetailedOutlineResult",
     "ForeshadowReview",
     "ForeshadowSuggestion",
@@ -91,6 +102,7 @@ __all__ = [
     "OutlineResult",
     "PaceIssue",
     "PaceReview",
+    "PolishResult",
     "Scene",
     "StyleDimension",
     "StyleDriftReview",
@@ -104,7 +116,10 @@ __all__ = [
     "book_title_spec",
     "brainstorm_spec",
     "character_gen_spec",
+    "continue_spec",
     "continuity_spec",
+    "de_ai_spec",
+    "expand_spec",
     "fine_outline_spec",
     "foreshadow_spec",
     "glossary_spec",
@@ -116,5 +131,6 @@ __all__ = [
     "refiner_spec",
     "style_drift_spec",
     "style_extract_spec",
+    "teardown_spec",
     "worldbuilder_spec",
 ]