feat(playground): explain noncomputational annotations in-app

[bachase]

Note

Prototype PR into the bc-cleanup-noncomputational-mvp feature branch — lighter review bar than main.

Pasting a circuit with LOSS or LEVEL_TRANSITION into the playground currently surfaces the raw C++ error, which tells users to "run the circuit through clifft.noncomp.sample" — a dead end in the browser (no noncomp entry in wasm, and no way to define a noncomp.Model from pasted text). This renders playground-appropriate guidance instead.

What changed

• NoncompNotice — one shared component: "Leakage & loss annotations (LOSS, LEVEL_TRANSITION) aren't supported in the playground. See the leakage & loss guide for the Python API." with the guide linked (external-link idiom matched to the app's existing one).
• Both surfaces the error reaches (traced, not assumed): the compile path (App.tsx — new scoped banner below the toolbar; general compile errors keep their existing rendering) and the simulate path (HistogramChart.tsx — one more branch beside the existing MemoryLimitExceeded special case; the Simulate button isn't gated on compile success, so a LOSS circuit reaches this path too).
• Detection: isNoncompAnnotationError in types.ts matches the C++ message on "noncomputational annotation", robust to which gate triggered it. The C++ message itself is untouched — it remains correct guidance on the Python/C++ surfaces.

Notes

• The guide URL (…/guide/leakage-and-loss/) was verified against mkdocs.yml (site_url + nav) and the live site's directory-URL convention; it 404s today only because the leakage guide exists solely on this feature branch — it resolves once the branch reaches main and docs deploy.
• No C++/wasm changes; no CMake churn.

Validation

• npm ci, npx tsc -b, npm run lint — clean (mirrors the CI playground job)
• npm run build — succeeds; grepped the bundle to confirm copy, URL, and detection string survived bundling
• pre-commit run --all-files — clean

🤖 Generated with Claude Code

[bachase]

Incorporated into #231