[TheGreatAxios]

Summary

• Replaced the checkbox fieldset in new-workbench-picker.tsx with a chip-based agent picker: removable chips for selected agents, a search popover ("+ Add agent") with keyboard nav (arrows/Enter/Escape), and a filled/checked state on selected options — restoring the design from Make the new-workbench composer intent-first #658.
• Added a "Create agent" entry at the bottom of the agent search popover that opens CreateAgentPanel inline; on successful deploy the new agent is auto-selected and the agent list is invalidated so it shows up immediately (restoring Add agent creation to the workbench composer picker #693, minus the removed template/invitable-definitions plumbing that no longer exists on this screen).
• Verified the scoped drawer overflow/focus-ring CSS and create-agent-panel class from Fix New Agent drawer clipping and scrollbar overlap #691 are already present on create-agent-panel.tsx/app.css in this branch — no changes needed there.

Verified

• bunx tsc -p apps/web --noEmit
• bun run lint
• bun run fmt
• cd apps/web && bun run build
• bun test apps/web/src (515 pass; 69 pre-existing failures unrelated to this change — document/window not defined in a subset of test files run outside their DOM harness, same failures reproduce on files this PR never touches)

Not verified

• No live dev-stack run (out of scope per instructions); did not manually click through the picker in a browser.

react-ui candidates

• The dismissable agent-search popover (useDismissablePopover + listbox/combobox markup) is generic enough to be a reusable react-ui component if another picker needs the same search-and-chip pattern.

[linear-code]

CL-8477