feat(cli): add --workspace filter to 'dispatch list'

The backend already supported GET /conversations?workspaceId= but the CLI
never sent it. Wire the list command to that filter:

- args.ts: parse --workspace / -w on 'list' (placed before the --catch-all
  so the single-dash -w shorthand isn't taken for a positional prefix);
  add workspaceId? to the list ParsedCommand.
- http.ts: add workspaceId? to FetchConversationsOpts; send ?workspaceId=
  (after q/status, preserving URLSearchParams order).
- main.ts: forward parsed.workspaceId into fetchConversations; update USAGE.

Composable with --status and the <prefix> short-id arg. 'Open conversations
in workspace X' is now: dispatch list --workspace X  (status defaults to
active,idle). No contract changes — purely additive CLI wiring.

Tests: +4 args (incl. composability + missing-value error), +2 http
(exact ?workspaceId= URL + combined status/workspaceId with %2C encoding).
typecheck EXIT 0, biome clean (364 files), full suite 1558 passed.
Live-verified against an isolated server.

0 files changed, 0 insertions, 0 deletions