[Feature] Deep linking — open a specific session via URL parameter

[anaypaul]

What

Support http://localhost:3458/?session=<session-id> to open a specific session directly.

Why

Makes it easy to share session links, bookmark interesting sessions, and link from other tools.

How

• Read ?session= from window.location.search in App.tsx or SessionList.tsx
• If present, call setActiveSession() + loadSessionMessages() on mount
• Update URL when user selects a session (using history.replaceState)

Complexity

Low — 1-2 hours.