Session picker: add star/pin, tags, and archive for managing many parallel sessions

Problem

Power users who run 10-30+ Claude Code sessions in parallel (one per task/feature) struggle to manage them in the current session picker (claude --resume).

The picker already has great features — search (/), rename (R), preview (P), and cross-project toggle (A) — but at scale, it becomes a flat, unsorted list that's hard to navigate.

Currently, I maintain a manual memo in a separate notes app to track which sessions are active and their categories:

## Product
- biz-lab-ui-effect
- biz-fv-width

## New Business
- new-ai-messenger
- new-ad-dashboard

## Low Priority
- fix-contact-edit

This works but feels like it should live inside the picker itself.

Proposed Features

1. Star / Pin

• Pin active sessions to the top of the picker
• Quick toggle (e.g., S key in picker)
• Pinned sessions always appear first, regardless of recency

2. Tags / Categories

• Assign tags to sessions (e.g., product, new-biz, priority-c)
• Filter by tag in picker (e.g., type #product to filter)
• Could reuse the / search with a # prefix convention

3. Archive

• Hide completed/stale sessions from the default picker view
• Toggle visibility (e.g., H key to show/hide archived)
• Keeps the picker focused on active work

Context

• Using a terminal multiplexer (cmux/tmux) with multiple tabs, each running a CC session
• When the terminal app closes, tabs disappear but sessions persist — the challenge is finding and resuming the right ones
• Named sessions (--name) + picker search help, but don't solve the "overview of all active work" problem at scale