Add collapsible section headers in session sidebar (Scheduled, Today, etc.)

Feature Request

Add the ability to collapse/expand grouped section headers in the Claude Code Desktop session sidebar.

Problem

When you have multiple scheduled sessions (e.g., automated watchers, daily digests, intake pipelines), the Scheduled section takes up significant vertical space in the sidebar. This pushes the actual working sessions (grouped by date — Today, Yesterday, etc.) below the fold, making it harder to find and switch between them.

Current behavior: All sections are always expanded with no way to collapse them.

Proposed Solution

Add a collapse/expand toggle (chevron icon or click-on-header) for each section group in the sidebar:

• Scheduled — collapse to hide all scheduled sessions
• Today — collapse to hide today's sessions
• Yesterday — collapse to hide yesterday's sessions
• (and any other date-grouped sections)

Details

• Clicking the section header (or a chevron icon) toggles collapse state
• Collapsed sections show just the header with a count badge (e.g., "Scheduled (5)")
• Collapse state should persist across app restarts (localStorage or similar)
• Default: all sections expanded (preserves current behavior)

Mockup

▼ Scheduled                    5     ← expanded (current default)
    Auto away mode          Manual
    Gtaa project intake     Manual
    Gmail intake            Manual
    Controlplane digest     Manual
    Github issue triage     Manual

► Scheduled                    5     ← collapsed (proposed)

▼ Today                        3     ← expanded
    Session 1
    Session 2  
    Session 3

Use Case

Power users with many scheduled automations (cron jobs, watchers, intake pipelines) need quick access to their working sessions without scrolling past a long list of scheduled tasks they rarely interact with manually.

Environment

• Claude Code Desktop on Windows 11
• 5+ scheduled sessions currently visible