ci(): vitest setup

[ShaMan123]

Description

This PR mirrors ThatOpen/engine_fragment#294 and acts as a prerequisit to #777

Changes: vitest/vite toolchain, config and setup file, jest removed.

[agviegas]

Merged, with a few things added on top.

First, thanks for the shape: node as the default environment with a documented per-file opt-in is exactly what we asked for on the fragments side, and the setup file guarding the canvas mock and the worker shim behind a window check is the right call.

Three amendments. passWithNoTests is now on, since the first suites arrive in #777 and until then a tree with no test files should not fail the run. ./src/**/example.ts had to be repeated in the dts plugin's exclude: that option overrides tsconfig-build's exclude rather than adding to it, so the example files came back into the dts pass and reported TS2307 for their doc-only imports. We verified it as a control, removing the line brings the errors back and restoring it clears them. And there is a .gitattributes pinning snapshots to LF, so running the suite on Windows does not dirty them.

One thing we added because the PR title deserved it: the repo had no CI at all, so a ci() change added no gate in practice. There is now a workflow that installs with a frozen lockfile and runs build-core, build-front and the suite on every pull request and push to main.

One finding for later, not a blocker: the vite 7 bump makes the dts pass type-check packages/core/vite.config.ts, which now prints TS6133: 'fs' is declared but its value is never read on every core build. The import really is dead, only used in commented-out code, so it is a one-line cleanup whenever someone is nearby.