v0.4.0 — rebuilt on vscode-ext-kit 3.x

Rebuilt on @kkdev92/vscode-ext-kit 3.x. Rendering, sanitisation, the worker
queue and the markdown-it plugin are untouched — what changed is how the
extension starts and stops. Diagrams render exactly as they did.

Breaking

• VS Code 1.125 or later is now required, up from 1.101. The framework's
  minimum cascades here. Installations on older versions keep 0.3.0 and stop
  receiving updates.

• plantumlLocal.logLevel is a floor, not the only filter. The output
  channel is a LogOutputChannel now, and VS Code decides what one of those
  shows — an extension cannot raise its own channel's level. The setting can
  still make the log quieter.

  To see debug, run Developer: Set Log Level and pick PlantUML Local.
  That is a per-channel level and it persists across restarts. In exchange the
  channel gains per-level colouring and the panel's own filter.

Changed

Activation is one declaration, validated before VS Code is touched: a duplicate
id or a missing dependency fails at import rather than half-registering at
runtime. The render worker and the debounced preview refresh are owned by the
framework and released on its single cleanup path, in reverse order, within a
shutdown budget.

extendMarkdownIt is declared rather than assembled by hand, which makes
activate asynchronous — VS Code awaits it before reading the contribution,
which is what the Markdown preview has always done.

Full changelog: https://github.com/kkdev92/plantuml-local/blob/main/CHANGELOG.md