fix(cos): prevent CoS panel width blowout when non-canvas avatar is active

[atomantic]

Summary

Fixes an issue where the Chief of Staff left panel expanded beyond its intended 320px column width after an agent completed a task, pushing the right column of stat cards (Pending, Issues, Queue Pause) outside the visible render area.

Root Cause

1. In ChiefOfStaff.jsx, when an agent is active with a dynamic 3D/canvas avatar style (e.g. cyber, sigil, esoteric, rigged), hasCanvasAvatar is true, and the avatar container applied lg:w-full.
2. When the agent finished the task, activeAgentMeta was cleared and avatarStyle fell back to configAvatarStyle (SVG).
3. SVG avatars set hasCanvasAvatar to false. The false branch lacked w-full / lg:w-full, rendering with lg:flex-none and unconstrained width.
4. Children with wide content or long event logs (such as the task cleanup logs emitted on completion) caused the flex container to size to their max-content width (~600px).
5. The stats grid inside the container scaled its 2 columns to ~300px each, causing column 1 to fill the entire 320px sidebar rail and column 2 to be clipped by overflow-x-hidden.
6. Once a new task began, activeAgentMeta was re-set, hasCanvasAvatar became true again, re-applying lg:w-full and snapping the pane back to 320px.

Fix

• Added min-w-0, w-full, and lg:w-full lg:max-w-full across the CoS sidebar rail, the collapsible agent panel, the inner avatar container (for both canvas and non-canvas branches), and child wrappers (stats grid and event log).
• Added regression test in client/src/pages/ChiefOfStaff.test.jsx asserting that non-canvas avatar styles retain w-full, max-w-full, and min-w-0 constraints on the desktop rail.