v0.51.0

The server held its whole lifecycle in four module globals - the registry, a restored flag, the pages seen and the pages owed - and a dozen free functions reading them. Every fixture that wanted a clean server rebuilt all four by hand, which is the tell of state that wants to be one thing with one lifecycle; the cost showed three times in one afternoon (#1324).

`Work` now owns it: declare, wake, look, act, remember, close, each one method, documented in the order it happens. The server builds one from `AIHAWK_SESSION_ID` and every tool goes through it; a test installs one of its own with a factory that launches nothing. `server.py` is 783 lines where it was 1231, with nothing added but the object.

A rebuild is no longer silent: `browser_navigate` says in front of its answer that the browser had died and was reopened as the same person, so a person watching the window close and reopen reads the same thing in the transcript.

And a dead browser is recognised by its type: invisible-playwright 0.15.0 raises one `TargetClosedError` for a disposed object and a closed pipe alike and exports it, so the three sentences 0.50.0 matched are gone and the floor moves to 0.15.0.

The address scanners read both modules now. Five known-bad mutations seen red. Suite 622 green, ruff, content and english gates clean. Version 0.51.0.