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>

.changeset/thread-list-active-default.md

@@ -0,0 +1,14 @@
+---
+"@united-workforce/cli": minor
+"@united-workforce/util": patch
+---
+
+feat(cli): `uwf thread list` now defaults to active threads only
+
+Changes the default behavior of `uwf thread list` to show only active threads
+(idle + running). Adds a new `--all` flag to opt into the previous behavior of
+listing every thread (including completed, cancelled, and suspended).
+
+When invoked with no flags, the command now hides completed/cancelled/suspended
+threads. Use `--all` to see them, or `--status <status>` to filter explicitly.
+The `--status` filter wins when both are present. Resolves issue #147.