Sidebar follow-ups: configurable session keys and daemon VCS cache

[aguil]

Context

Follow-ups from #7 (sidebar agents panel + session cards).

Tasks

1. Configurable session shortcut keys

Sidebar session labels should match prefix + s session picker keys, including custom -K mappings.

Plan: tmuxr/plans/session-shortcut-keys.plan.md (local workspace)

Proposed rollout:

• Phase 1: work config key session-shortcut-keys (default stock tmux alphabet)
• Phase 2: optional @work-session-shortcut-keys tmux global (sync with dotfiles -K binding)
• Phase 3: optional session-shortcut-index: choose-order when $N-based labels drift from choose-tree list order

Dotfiles default alphabet (Jason's current -K mapping):

0123456789abcdegiopu

2. Cache/throttle daemon VCS enrichment

Code review finding: performance-enrich-tree-daemon-poll

aggregateState() runs enrichTree() for every tree on each daemon poll (~2s), spawning jj/git subprocesses per tree. Acceptable for initial merge; optimize if CPU/latency becomes noticeable.

• Measure poll cost with multiple jj/git trees
• Add caching (mtime/branch hash) or slower refresh interval for tree metadata
• Keep sidebar responsive when cache is stale

References

• PR feat(sidebar): agents panel, session cards, and Nerdfont status glyphs #7
• Code review run code-review-20260709155217-5a61c408 (finding performance-enrich-tree-daemon-poll)