feat(app): add persistent session list panel

[palomitaschilango]

Adds a persistent session list panel to the web app that shows all available sessions and allows quick navigation between them.

Changes

• New \SessionListPanel\ component with session listing, current session highlighting, and navigation
• Toggle button in titlebar (icon: menu) with \mod+shift+s\ keybinding
• Collapsible left panel (280px) integrated into the session view layout
• Panel state managed via layout context (non-persisted, ephemeral)

[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR that might overlap with this feature:

Related PR:

• PR feat(app): add subagents tab to the session side panel #39382: feat(app): add subagents tab to the session side panel

This PR also adds a panel to the session view and might have overlapping UI layout changes. You should verify if both PRs are working on different aspects of the session panel or if there's any conflicting work.

All other search results either returned the current PR (#39659) itself or unrelated features like Todo Sidebar, MCP Apps, or team TUI integration.