fix(cli): report compile diagnostics in the check report

[miguel-heygen]

What

bundleToSingleHtml takes an optional diagnostics sink. hyperframes check passes one and renders a Compile section, in the human report and in --json.

Why

The bundler emits three warnings as bare console.warn calls:

code	what it reports
color_grading_lut_not_inlined	a LUT that could not be inlined, so the bundle is not self-contained
static_guard_contract	a StaticGuard contract breach on the compiled entry
sub_composition_skipped	a sub-composition that could not be resolved and was dropped

None of them reached the structured report. A --json consumer could not see them at all, and a terminal reader had to catch them scrolling past above the report they were reading. All three describe something wrong with the artifact you are about to ship.

How

The sink follows the onMissingComposition hook inlineSubCompositions already uses, so this is an existing pattern rather than a new one. Records carry code, severity, message and an optional source, and become CheckFindings through findingAtRoot -- the same helper motion_spec_invalid and check_runtime_failure already use.

source rather than a line number: none of the three sites carries a source position, and synthesising one would be a fabrication. All three do know a path, so that is what they report.

Three deliberate limits:

• Nothing changes for existing callers. The sink is optional; without one these still console.warn with byte-identical text. A test pins both the identical warn calls and a byte-identical bundle string between the sink and no-sink runs.
• Compile counts stay out of the aggregate totals, so --strict fails nothing it passes today. This changes what you can see, not what passes.
• The section carries reached, because an empty findings list is otherwise ambiguous. runCheckPipeline short-circuits before bundling whenever lint has errors, so "clean" and "never ran" must not print the same thing. It prints not reached (fix lint errors first) instead. It is also false when the browser check throws after bundling, which would otherwise report reached: true with zero findings.

Own section rather than folded into runtime: different phase, and folding would have moved runtime.warningCount for existing --json consumers. compile is a purely additive key.

Test plan

• Unit tests added/updated
• Manual testing performed
• Documentation updated (if applicable)

Core 99 files / 1697 tests, CLI 175 files / 2490 tests, bun run lint exit 0, bun run build (cross-package typecheck) exit 0.

Verified on a lint-clean probe rather than by reading the code. The LUT warning appears in the Compile section and in the --json envelope. Removing data-width from the same probe makes lint fail, and the section then correctly reads not reached.

Tests were mutation-tested rather than trusted green. Five mutants: sink ignored, source dropped, double-reporting to both sink and console, reached defaulting true, and compile warnings folded into the aggregate. All five were killed.

Every bundleToSingleHtml call site was enumerated. runBrowserCheck and bundleWithLocalizedFonts collect; captureFindingCrops deliberately does not, since it re-bundles the same project and would duplicate. Snapshot, studio server, validate, layout, compare, grade-compare, motionShot and the studio vite adapter all keep the console.warn default with no signature change. Producer has no production use of this function.

Not covered

static_guard_contract fires only when lint has errors, so it is structurally unreachable through check -- the lint short-circuit always beats it. It reaches the sink for studio, preview and render callers. Left as is; making it reachable means restructuring the short-circuit, which is a behaviour change with its own blast radius.

sub_composition_skipped is arguably an error rather than a warning for a render, since you ship a bundle silently missing a scene. Severity is deliberately unchanged here -- this PR is about visibility, not about changing what passes.

No telemetry field for the compile section. trackCheckReport takes a flat props object and never the CheckReport type, so the shape change cannot break it.

Producer and studio suites were not run; the cross-package bun run build typechecks them. The studio dev server and vite preview were not exercised live.