fix(sidebar): trim working badge label and name working agents in tooltip

[tellaho]

Overview

Category: improvement
User Impact: The sidebar "working" pill no longer crowds out the channel name, and hovering it now says in plain prose who's working — e.g. Ned and 2 agents working.

Problem: The sidebar channel-row working pill rendered a Working · 3s label that ate horizontal room, forcing the channel name to ellipsize too early (buzz-channel-indicat…). There was also no way to tell who was working without opening the channel.

Solution: Trim the pill to a bare elapsed time (3s single-agent, 4m 3s (2) multi-agent) so the channel name keeps its room, and move the "who" into the native hover tooltip. The tooltip uses one cohesive prose rule — name at most one agent and count everyone else as agents — so it stays narrow no matter how many agents work or how long their names are, and reads naturally rather than as a list.

File changes

desktop/src/features/sidebar/ui/SidebarSection.tsx
Trims the visible pill label to bare elapsed time and adds formatWorkingTooltip, which drives the row's title. Implements the cohesive labeling rule: one resolved name max, then N agent/N agents for everyone else (known overflow and unknowns alike).

desktop/src/features/sidebar/lib/useActiveWorkingChannelsById.ts
Resolves working agent pubkeys to managed-agent names for the tooltip; unresolved pubkeys are dropped from the name list so they fold into the count rather than ever surfacing raw hex.

desktop/src/features/agents/activeAgentTurnsStore.ts
Surfaces the set of working-agent pubkeys per channel (agentPubkeys) so the sidebar can resolve names — additive, no consumer impact.

desktop/src/features/sidebar/ui/SidebarSection.test.mjs
Covers the six tooltip spec cases: one known, named+1 (singular), named+2+ (plural), all-unknown singular, all-unknown plural, and mixed known/unknown.

desktop/src/features/sidebar/lib/useActiveWorkingChannelsById.test.mjs
Covers the pubkey→name resolution path, including case-insensitive matching and the unresolved-drop behavior.

desktop/src/features/agents/activeAgentTurnsStore.test.mjs
Asserts agentPubkeys is aggregated correctly per channel.

Reproduction Steps

1. Run the desktop app with at least one channel that has an actively working agent.
2. Look at the sidebar channel row: the working pill now shows just the elapsed time (e.g. 3s, or 4m 3s (2) when multiple agents are working), and the channel name no longer ellipsizes early.
3. Hover the pill: the native tooltip reads as prose — Ned working, Ned and 1 agent working, Ned and 2 agents working, or 3 agents working when no name resolves.

Notes

• The tooltip is a native OS title attribute, so it isn't DOM-renderable and can't be captured in a screenshot.
• "agent"/"agents" is the only count noun, chosen so the label never reads as if humans could appear there (humans don't show in this surface).

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Coordination: buzz://message?channel=e325a47e-d11d-4f16-8e2d-0c55a2d924bb&thread=a9d0d732b58d87849405cb38fc18efc9e75a03af273abf3bf4d94ae583a7b174