fix(web): code blocks scroll inside the transcript column (CL-8509)

[TheGreatAxios]

Summary

• A long fenced code block in a chat or workbench transcript message (e.g. a printed package.json) could push the message column wider than the pane, with no horizontal scroll.

Changes

• .chat-md-code-block (the <pre> wrapper the markdown renderer emits for fenced code) now caps at max-width: 100% alongside its existing overflow-x: auto, so a long line scrolls inside the block instead of widening the ancestor flex chain.
• .chat-md-inline-code gains overflow-wrap: anywhere so an unbroken inline-code token (path, hash, URL) wraps within the message column instead of forcing it wider.
• Both the chat thread (apps/web/src/pages/chat-thread-page.tsx) and workbench room (apps/web/src/pages/workbench-room-page.tsx) transcripts share the same Markdown renderer and chat-md-* styles, so one CSS fix covers both.

Testing

• bun run check (typecheck, lint, fmt, test) passes.

[linear-code]

CL-8509