v0.5.0

• Add RESPONSE to observe requests made by the browser, with status, header, JSON Pointer assertions, and response captures.

• Add named popups with POPUP, explicit tab selection with TAB, CLOSE, and tab:name closed assertions.

• Add frame: locator segments for cross-origin and nested iframes in actions, assertions, and captures.

• Allow selected browser installation and add whirl doctor with repair commands.

• Add JSON check diagnostics, stable error codes, runtime report metadata,
  and --rerun-failed for complete failed flows and their setup.

• Add a runnable sample shop and a CI task with reports and failure artifacts.

• Keep actionability details in failures and add whirl show-trace.

• Reject input paths that select no flow files.

• Preserve presence assertions before checks that accept an absent element.

• Bound shim lifecycle operations and request writes so an unresponsive shim
  cannot stall a run indefinitely.

• Move filesystem preparation off async workers and improve worker shutdown.

• Accept a popup closing during a click only when its target received the
  click; a closure before delivery still fails.

• Add opt-in diagnostic logging through WHIRL_LOG, with sensitive values
  excluded from log fields.