feat(memory): Obsidian-style live Markdown notes in Memory & Collaboration

[PeterGuy326]

Product intent

Turn Memory & Collaboration → Position Documents / Shared Knowledge from a read-only document browser plus modal/manual editing into an Obsidian-style, filesystem-first note workspace.

This is a focused follow-up to #347 / #505. #505 supplies the safe document lifecycle and write seam; this issue owns the live note-editing interaction and should land after that prerequisite rather than expanding #505 during review.

User experience

• Selecting a Markdown note opens it directly in an editable note surface; reading and editing are one continuous experience, not separate viewer and textarea pages.
• Support source/edit, reading, and live-preview modes. Markdown structure should stay legible while typing.
• Autosave local edits after a short idle debounce and show truthful states: 已保存, 正在保存…, 未保存, 保存失败, 外部修改冲突.
• Preserve cursor, selection, active note, scroll position, and draft when switching the source sidebar, employee, focus mode, or returning to the module.
• Cmd/Ctrl+S forces save; save failures never discard the draft.
• Detect filesystem changes made outside RoleWeave and refresh clean documents. If the local editor is dirty, do not overwrite it: surface a compare/reload/keep-mine conflict choice.
• Support Obsidian-style [[wikilinks]] and normal Markdown links. Clicking an internal note link opens the target in this workspace; missing targets offer safe note creation.
• File and link affordances use meaningful icons by target type (Markdown note, folder, web link, attachment, missing note) and remain keyboard accessible.
• Keep the existing file list/search and allow create/rename/archive/delete from feat(knowledge): document lifecycle ops for Knowledge Base #505 without losing an active draft.

Authority and storage boundaries

• Markdown files remain the source of truth on disk; do not create a second hidden note database.
• Use the existing validated position-document APIs from feat(knowledge): document lifecycle ops for Knowledge Base #505. Preserve path traversal, symlink, byte-limit, workspace/position ownership, and atomic-write protections.
• Bound package files such as SKILL.md and non-knowledge/* files remain read-only unless the existing authority contract explicitly permits writes.
• A write must carry the version read by the editor (or equivalent compare token). The server rejects stale writes instead of silently overwriting external changes.
• Autosave is per file and serialized; late responses from a previous employee/file must not mutate the current editor.

Acceptance criteria

• Markdown note opens in an inline editable surface with source/live-preview/reading modes.
• Editing triggers debounced autosave and visible truthful save state.
• Cmd/Ctrl+S performs an immediate save.
• Switching views and returning preserves unsaved text and cursor/scroll state.
• External clean-file changes refresh; dirty-file changes produce an explicit conflict flow.
• Stale-version writes are rejected and covered by server tests.
• [[wikilinks]] and relative Markdown links navigate between notes; missing-note creation is explicit.
• Links include correct target icons and accessible names/focus behavior.
• Agent and external filesystem edits converge through the same file/version contract.
• Full renderer, server, IPC, i18n/CJK, packaging, and macOS/Windows verification remain green.

Dependency and delivery sequence

1. Review and merge feat(knowledge): document lifecycle ops for Knowledge Base #505 (document write/lifecycle contract).
2. Rebase this implementation on the resulting main.
3. Deliver this issue as a separate focused PR with exact-head review.

Refs #347
Depends on #505