fix: preserve drafts, canvas edits, and remote Continue tools

Keep paragraph formatting and checklist todos when removing canvas pages,
and preserve accepted undo/redo history after oversized input is rejected.
Merge restored queued text into the latest conversation draft and retain
image delivery when OCR returns image references and generated warnings only.

Deliver session MCP servers to bridged remote Continue Execute while keeping
Ask read-only and preserving local model-profile isolation. Add regression
coverage and update feature documentation. Correct stale conversation-limit
and forced-color assertions and the measured Electron layout test deadline.

Validation: 4,826 tests passed, 67 skipped; full typecheck and lint passed.
Current-source Linux x64 Execute/Ask/Execute MCP delivery passed, using 10
real text-provider requests and no image-provider requests. Image generation
itself was not exercised. Staged whitespace checks passed before commit.

Release note: 修复恢复队列时覆盖新输入、画布删页丢失清单格式及超限输入清空撤销历史的问题；图片 OCR 无正文时保留原图发送方式，远程 Continue Execute 正确保留会话 MCP 工具。

docs/features/document-processing/changed-paths.md

@@ -11,6 +11,8 @@ src/main/context-manager.ts
 src/main/context-manager.test.ts
 src/main/conversation-attachment-storage.ts
 src/main/conversation-attachment-storage.test.ts
+src/main/document-extracted-text.ts
+src/main/document-extracted-text.test.ts
 src/main/document-parsing-service.ts
 src/main/document-parsing-service.test.ts
 src/main/document-parsing-settings-store.ts
@@ -92,6 +94,7 @@ docs/features/document-processing/chat-attachments-technical-design.md
 docs/features/document-processing/implementation.md
 docs/features/document-processing/progress.md
 docs/features/document-processing/changed-paths.md
+docs/quality/recurring-defects.md
 ```
 
 `scripts/paddleocr-vl-probe.mjs` 和导航 README 原有未提交内容保留，本轮未修改。