🔊 feat!: make the three silent failures loud

Every change here answers one question: where does cereale currently fail
without saying so?

**Vite 8 / Vitest 4 drop decorators silently.** Both transform with oxc,
which does not implement the standard decorator transform and does not
report that. `vitest` prints "0 test" beside a bare SyntaxError, and
`vite build` reports success while emitting a bundle that throws on first
import. Ship the plugin that fixes it as `cereale/vite`, transforming with
esbuild and falling back to tsc — cereale depends on neither. The library's
own suite now runs through it, so it is exercised by every test.

**Legacy decorators died opaquely.** With `experimentalDecorators: true`,
still the default in most existing TypeScript projects, decorators are
invoked as (prototype, "name") and cereale raised "TypeError: Cannot convert
undefined or null to object". All decorators now resolve metadata through
one checkpoint that names the tsconfig setting instead, and reject
application to a method, getter or accessor field.

**Values JSON cannot carry were emptied.** A populated Map serialized to
{}, a Uint8Array to index-keyed noise, a bigint straight through so the
caller's own JSON.stringify threw somewhere unrelated. All now raise
JsonMappingError naming the property path and both ways out. Covers what a
@JsonSerialize serializer returns, sync or async. Circular-reference and
depth errors name the path too.

Also fixed: defineRule on a subclass with no decorators of its own wrote
the rule into its base class, because the base's metadata object is
inherited through the static prototype chain and `??=` found it non-nullish.

The README's toolchain table (tsc, esbuild, swc ✅, oxc ❌) is now executed
by a test rather than asserted, and the positioning leads with
class-validator + class-transformer, the stack cereale actually replaces,
rather than Zod, which it deliberately is not.

193 -> 249 tests.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SAcqrz3FcadkYr3xG32CjK

.github/workflows/ci.yml

@@ -37,5 +37,7 @@ jobs:
       run: |
         node --input-type=module -e "import * as m from './dist/esm/index.js'; if (typeof m.toInstance !== 'function') throw new Error('ESM entry point broken');"
         node --input-type=commonjs -e "const m = require('./dist/cjs/index.js'); if (typeof m.toInstance !== 'function') throw new Error('CJS entry point broken');"
+        node --input-type=module -e "import { standardDecorators } from './dist/esm/vite.js'; if (standardDecorators().enforce !== 'pre') throw new Error('ESM cereale/vite broken');"
+        node --input-type=commonjs -e "const { standardDecorators } = require('./dist/cjs/vite.js'); if (standardDecorators().enforce !== 'pre') throw new Error('CJS cereale/vite broken');"
     - name: Run Demo
       run: npm run demo