Session permission state should persist per-session (not per-project)

[smirki]

Description

The auto-approve/permission state for agent actions (e.g., "allow all file writes", "allow shell commands") is currently scoped to the project level. It should be scoped per chat session instead, so different sessions can have different permission levels.

Code Reference

• app/src/components/chat/ChatContainer.tsx:110-145 - permission state management

Current Behavior

When a user enables auto-approve in one session, it affects all sessions in the same project. This is a security concern - a user might want strict approval in one session while being permissive in an experimental session.

Expected Behavior

• Permission state (auto-approve for file writes, shell commands, etc.) is scoped to individual chat sessions
• Each session starts with default permissions
• Changing permissions in one session doesn't affect others
• Permission state persists within a session (survives page reload)

Acceptance Criteria

• Permissions are per-session, not per-project
• Default permissions apply when creating new sessions
• Permission changes in one session don't leak to others
• State persists across page reloads for the same session