[TheGreatAxios]

Summary

• Extracted a single Composer (apps/web/src/chat/composer.tsx) used by both the standalone chat thread page and the docked/sub-thread composer in the workbench room page, replacing two near-identical local copies. Behavior is unchanged: Enter sends, Shift+Enter inserts a newline, disabled with the " is starting…" placeholder while no run is live, sends go through the existing startChat/replyInChat/sendToRoom mutations.
• Added a right-hand action rail with a Send button (icon button, spinner while pending). No Stop action: neither apps/web/src/chat/threads-api.ts nor the hub API expose a way to cancel a running turn, so cancellation is left out of the rail with a comment pointing at where to add it once that capability exists.
• Raised transcript (.chat-thread-body) and composer text to a 16px minimum via max(var(--text-base), 16px) plus var(--font-weight-medium), following the same shared-token approach used previously in the deleted packages/chat-ui/src/styles.css.

Verified

• bunx tsc -p apps/web --noEmit
• bun run lint (pre-existing warnings only, in apps/sidecar, unrelated to this change)
• bun run fmt (no changes needed)
• cd apps/web && bun run build
• cd apps/web && bun run test — 584 pass, 0 fail

Not verified

• No dev server was started per instructions; not manually clicked through in a browser.

Flag for corbitsdev/react-ui

This composer (text field + grouped send/stop action rail, transcript typography tokens) looks like a good candidate to lift into corbitsdev/react-ui as a reusable component, per AGENTS.md's rule that reusable UI belongs there.

[linear-code]

CL-8476