fix(web): polish Research workspace drawer UI for Saved/Memory tools

[jerry609]

Parent Epic

#159 — [Epic] Obsidian CLI 集成 — 研究知识管理

Summary

The new Research workspace drawer needs UI polish so Saved/Memory tools feel like a coherent side workspace instead of a raw nested modal stack.

Problems

• drawer header hierarchy is too flat
• tabs do not read like a workspace switcher
• spacing and scroll behavior are cramped when Saved + Obsidian tools are present
• the drawer should carry active scope context more clearly

Acceptance Criteria

• Drawer header includes a clearer title/description and active scope context
• Saved/Memory tabs read as a deliberate workspace switcher
• Content region scrolls cleanly without crowding the header
• Obsidian handoff panel remains usable on narrow widths
• Browser verification covers drawer open, tab switch, and Obsidian dialog flow