feat(cli): thread list defaults to active threads only

Closes #147. Changes default behavior of `uwf thread list` to show only
active threads (idle + running). Adds `--all` flag to opt into the
previous full-list behavior. Explicit `--status` still wins over `--all`.

- cmdThreadList gains a `showAll: boolean` parameter (default false)
- CLI registers `--all` option and passes it through
- Test suite includes new `default behavior (issue #147)` describe block
  covering 9 scenarios; existing tests updated where they implicitly
  relied on the old "show everything" behavior
- README, cli-reference, and usage-reference updated to document the
  new default and the `--all` flag

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/util/src/cli-reference.ts

@@ -29,8 +29,9 @@ uwf thread exec <thread-id>                       # execute one moderator→agen
                [-c, --count <number>]             # run multiple steps (default: 1)
                [--background]                     # run in background
 uwf thread show <thread-id>                       # show thread head pointer
-uwf thread list                                   # list threads
-               [--status <status>]                # filter: idle, running, or completed
+uwf thread list                                   # list active threads (idle + running)
+               [--all]                            # include completed/cancelled/suspended
+               [--status <status>]                # filter: idle, running, suspended, completed, cancelled, active
 uwf thread read <thread-id>                       # render thread context as markdown
                [--quota <chars>]                  # max output characters (default 32000)
                [--before <step-hash>]             # load steps before this hash (exclusive)