v0.2.26: modernise the test stack and drop its dead weight - #290

The vitest config carried a `configLoader: 'native'` warning on every run and a
pair of esbuild options the oxc transformer ignored outright, plus a disabled
Storybook project whose only purpose was a stale comment. All of it is gone:

- `import.meta.dirname` replaces the hand-rolled `__dirname` guard, which is the
  form the native config loader supports.
- The dead `esbuild` blocks are removed; oxc handles JSX natively.
- The disabled Storybook project block is removed; nothing ran it and the
  scaffolding it referenced (`vitest.shims.d.ts`, `@vitest/browser`,
  `@vitest/ui`) is deleted with it. Storybook itself is untouched.

`pool` stays at the default rather than `vmThreads`: vm pools cannot inline the
CJS `three` family that `@react-three/drei` requires (the suite's CJS interop
throws "Cannot use import statement outside a module" under them), and
`isolate: false` reuses one jsdom for everything but leaks state and failed
11 tests across 4 files. The ~16.7s of worker startup the reporter estimates
remains unclaimed, and `THREE_CJS_DEPRECATED` still prints once -- both are
properties of the upstream three/drei CJS entries, not of the config.

Verified unpiped by exit code: `biome check`, `type-check`, `test:ci`
(269 tests, 35 files; coverage unchanged and above thresholds), `build`,
`check:bundle` within budget, and `test:e2e:smoke` (server raised, smoke
passed, server stopped).