docs: task #18 mechanical delete batch (Phase 1) — en-US + web/docs + 22 obsolete zh-CN source docs (#1642)

Per PM task #18 msg=5f300de5 + user msg=f3051291 scope lock + PR #1637 Section 4 triage matrix:

### docs/en-US/** 全删 (~30 files)
Per user msg=f3051291 "英文文档可以全部删除"。全量移除 en-US 目录。

### web/docs/** 全删 (~16 files)
Per user msg=f3051291 "Web 中的文档可以全部删除"。全量移除 web/docs 目录(含 en-US + zh-CN 镜像)。

### docs/zh-CN/ 废弃 source docs (22 files)

blueprint PR #1637 Section 4 triage matrix 标 DELETE 或已 MERGE 到 consolidated target 的 source docs。此 Phase 1 batch 只删已对应 target merge 完成的 source(task #8/#9/#13/#14/#16 对应 source + unconditional DELETE items);Phase 2 将在 Bryce task #10/#11/#12/#15 merge 后补删其 source docs。

**DELETE-only (历史/过程 doc 无对应 consolidated target)**:
- agent-backend.md (superseded by agent_runtime_v3.md → conversation-agent-evaluation.md task #9)
- connected_components_optimization.md (历史优化 log)
- graph_db_abstraction.md (M1-M3 已落地设计文档)
- graph_normalization_merge_full_analysis.md (历史 audit)
- graphindex_rewrite.md (重构 log)
- lightrag_refactor.md (重构计划)
- prompt_customization_integration_todo.md (TODO 已全部 shipped)
- qdrant_memory_optimization.md (运营历史优化)
- tag_based_permission_design.md (feature 未实装 per Bryce grep-verify + PM msg=4a73b5a4 lock)
- vector_db_abstraction_m2_pr.md (PR 过程 doc)
- vector_db_abstraction_m3_pr.md (PR 过程 doc)

**MERGE 已完成 (target task 已 merge)**:
- architecture.md → architecture/overview.md + domains.md (task #8 PR #1640 merged)
- agent_runtime_v3.md → architecture/conversation-agent-evaluation.md (task #9 PR #1641 merged)
- chat_history_design.md → architecture/conversation-agent-evaluation.md (task #9 PR #1641)
- evaluation-design.md → architecture/conversation-agent-evaluation.md (task #9 PR #1641)
- prompt_customization_design.md → architecture/conversation-agent-evaluation.md + admin-guide/prompt-customization.md (task #9+#14)
- prompt_customization_api_test.md → reference/prompt-api.md (task #14 PR #1641)
- url_and_text_import_design.md → user-guide/content-import.md (task #13 PR #1638 merged)
- document_upload_design.md → user-guide/document-upload.md + architecture/indexing-retrieval-kg.md (task #13 user-facing part merged; architecture part pending Bryce task #11)
- collection_knowledge_export_design.md → user-guide/knowledge-export.md (task #13 PR #1638 merged)
- reference/evaluation-current-guide.md → user-guide/evaluation-guide.md (task #16 MOVE merged)
- reference/how-to-configure-ollama.md → deployment/llm-providers-ollama.md (task #16 MOVE merged)

### 未删除 (Phase 2 pending Bryce task #10/#11/#12/#15 merge)

以下 source docs 对应 Bryce 正文任务仍未 merge,保留至 Phase 2:
- authentication.md (→ task #10)
- quota-system-design.md (→ task #10 + task #15)
- collection_marketplace_design.md (→ task #10 + task #15)
- indexing_architecture.md / vector_db_abstraction.md / search_flow_design.md / vision_index_creation.md / graph_curation.md / graph_index_creation.md / lightrag_entity_extraction_and_merging.md (→ task #11)
- web-search-design.md (→ task #12)

### Scope discipline
- docs/modularization/** 保留 (per PM msg=5286eb6a)
- README* 保留 (per user msg=f3051291)
- docs/zh-CN/rewrite-plan.md 保留 (task #4 deliverable)
- docs/zh-CN/reference/HOW-TO-DEBUG.md 保留 (task #16 KEEP)
- integration/mcp-api.md + integration/dify.md + deployment/build-docker-image.md + development/development-guide.md 保留 (task #17 + task #8 分别处理)

**Summary**: 113 files changed, 27713 deletions, 0 additions。

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: earayu