v0.4.0

A maintenance release. The timeline panel stays fast with a full buffer, the
live inspector stops walking the whole page, and several failures that used to
pass silently now say so. Releases are published from CI now.

Added

• Verbose render layer. lit-html's per-part debug events (template
  instantiation, set part, each binding commit) go to a new "Lit Render
  (verbose)" layer. It is off by default, because it fires once per binding on
  every render. Values are summarized as strings (string:"…", node:<li>,
  template, function:onClick) and never passed through.
• Releases from a version tag. Pushing a v* tag runs the CI gate, checks
  the tag against package.json and CHANGELOG.md, publishes to npm over
  trusted publishing (OIDC), and creates the GitHub Release from the changelog
  section. Prereleases go to the next dist-tag.

Changed

• The timeline list renders only the visible rows, through
  @lit-labs/virtualizer. A 2500-event recording keeps about 75 rows in the
  DOM instead of one per event. Filtering reruns only when the events or
  filters change.
• Live inspector mode no longer re-walks the page on every mutation.
  Batches with no custom element or shadow root in them are dropped, and
  relevant batches walk only the subtrees they added.
• The docs site was rewritten in plain language, with a tutorial, task-sized
  DevTools guides, a troubleshooting page, screenshots in both themes, and the
  Lit Design System's colours and type.

Fixed

• The source overlay's default hotkey is Ctrl+Shift+S, as documented. The
  runtime used to fall back to e, which also collided with the DevTools pick
  command.
• The source overlay removes its HMR listeners when it disconnects. Moving the
  element used to register the toggle twice, so the Vite DevTools overlay
  command did nothing, and a removed overlay kept reacting.
• urlSheet() and ?css-sheet warn when a stylesheet fails to load, and treat
  non-ok responses as failures. A 404 used to hand Vite's fallback page to the
  sheet as CSS, with a clean console. The sheet keeps its last good CSS.
• An unknown LIT_PLUGIN_HMR_ON_INCOMPATIBLE value logs a warning and falls
  back to the default, instead of quietly acting as reload.
• The Lightning CSS pass over css literals finds them by parsing the module,
  so css-tagged text inside a string, a comment, or another template literal
  is no longer rewritten.