feat(mnote-web): add local file read support to mnote.doc.fetch + WS push design doc

## mnote.doc.fetch: local file path support
- Detect local file paths (starting with `/` or `./`) and bypass Convex aggregate
- Read .md file directly via fs::read_to_string
- Return source: "local_fs" in response
- Support maxChars truncation for local files
- Online Convex path unchanged

## Design: WS push migration (3-14)
- New: design/03-rust-web/process/3-14-rust-web-tree-realtime-ws-push-v1.md
- Documents commit 9d8e361e WebSocket push migration rationale,
  architecture, and verification

## Updated design doc references
- 3-3: Mark SSE as fallback transport (WS push is primary)
- 08 checklist: Note WS push in Tree Realtime section
- AGENTS.md: Update tree/realtime references to reflect WS push

## Housekeeping
- desktop-hot.js: remove 3 stale log messages about disabled services
- page_ai_workflow.rs: fix 5 warnings (unused import, dead_code)

design/10-review/process/08-kernel-architecture-next-priority-review-and-checklist.md

@@ -330,8 +330,9 @@ node scripts/task122-rust-web-create-page-ui-smoke.js
 
 ### 3.4 Tree Realtime Live Cache
 
+- [x] 2026-05-17 WS push 迁移（`57ec8322`）：`/api/realtime/ws` 成为主 transport，SSE 降级为 fallback。mutation 后通过 `stream_delta_tx` broadcast channel 推送 delta，WS 客户端零 Convex 查询。
 - [x] 盘点 Sidebar、Page Tree、File Tree、page subtree 仍依赖 query/refetch/freshness 补偿的位置。
-- [x] 确认 `/api/tree/events` snapshot / delta / resync payload 覆盖 page/file/resource row。
+- [x] 确认 `/api/realtime/ws`（主）和 `/api/tree/events` SSE fallback 的 snapshot / delta / resync payload 覆盖 page/file/resource row。
 - [x] 新建页面后，双浏览器 A/B 检查另一端无需刷新出现页面。
 - [x] 重命名页面后，双浏览器 A/B 检查 Sidebar / Breadcrumb / File Tree 一致更新。
 - [x] 移动页面后，双浏览器 A/B 检查 tree order 不回闪。