docs(02-03): complete zhihu adapter plan

- ZhihuAdapter supports answer and zhuanlan content extraction
- Cookie-based authentication with login page detection
- Markdown output with YAML frontmatter
- 13 new tests, all 35 platform tests passing
- Test coverage: 86%

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.planning/STATE.md

@@ -4,14 +4,14 @@ milestone: v1.0
 milestone_name: milestone
 current_plan: 3
 status: executing
-stopped_at: Completed 02-01-PLAN.md
-last_updated: "2026-03-13T10:15:54.911Z"
+stopped_at: Completed 02-03-PLAN.md
+last_updated: "2026-03-13T10:27:09.681Z"
 last_activity: 2026-03-13
 progress:
   total_phases: 4
-  completed_phases: 1
+  completed_phases: 2
   total_plans: 6
-  completed_plans: 4
+  completed_plans: 6
   percent: 8
 ---
 
@@ -58,6 +58,8 @@ Progress: [█░░░░░░░░░] 8%
 | Phase 01-foundation P01 | 5 | 3 tasks | 3 files |
 | Phase 01-foundation P03 | 8 | 5 tasks | 7 files |
 | Phase 02-platform-skills P01 | 5 | 3 tasks | 5 files |
+| Phase 02-platform-skills P03 | 7min | 3 tasks | 4 files |
+| Phase 02 P02 | 8 | 4 tasks | 7 files |
 
 ## Accumulated Context
 
@@ -77,6 +79,8 @@ Recent decisions affecting current work:
 - [Phase 01-foundation]: 错误类包含 step_name, input_summary, suggestion 用于调试
 - [Phase 02-platform-skills]: 使用 dataclass 定义 ParsedLink，短链解析使用 requests.head
 - [Phase 02-platform-skills]: 无法识别的 URL 返回 None 而不是抛异常，便于调用方处理
+- [Phase 02-platform-skills]: Lazy import of kb_zhihu_metadata to avoid dependency issues
+- [Phase 02-platform-skills]: Login page detection via title keywords and content length threshold
 
 ### Pending Todos
 
@@ -92,6 +96,6 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-03-13T10:15:54.910Z
-Stopped at: Completed 02-01-PLAN.md
+Last session: 2026-03-13T10:26:42.175Z
+Stopped at: Completed 02-03-PLAN.md
 Resume file: None