Release notes.

docs(release-notes): 1.18.8 ships, and Steam catches up on eight tags

1.18.0 was the last Steam post, so the Steam note rolls up 1.18.1 through
1.18.8: Tessa drives the Shoebox sandbox end to end, the chat window becomes a
window you can select from, resize, zoom and reopen, and phantoms and error
nodes now say what they are through motion rather than color alone.

Web and Studio get roll-up entries too. Web 3.177.5 is the honest-charts
release: all 32 Insights charts rebuilt against the current telemetry after the
old queries were found rendering plausible but wrong numbers, plus a node
metering fix that had been under-counting multi-grid accounts. Studio 1.4.3 is
the rename and nothing else user-facing.

What is deliberately absent:

- Replay and time travel. The reference docs still say time travel is disabled
  while replay is reworked, and a lot of this range is SP-061 replay work.
  Announcing it would contradict a page we publish.
- Direct3D 12. It did not ship; the switch is parked as PR 3695 because it did
  not move the frame rate and broke the build gate.

whats-new.md also gains June and July, which were never recorded, and retires
its oldest highlight block.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>