Delete FullReportOnly: let selfContainedReportStrip alone control what self-contained reports render

[Romex91]

FullReportOnly is a second, parallel mechanism for the exact thing selfContainedReportStrip already does: decide what a self-contained report may show. The strip removes artifact-path fields from the measurement; FullReportOnly then separately hides the UI that would have rendered them. Two sources of truth for one decision, and they must be kept in sync by hand — a stage that adds a stripped field but forgets the <FullReportOnly> wrapper (or vice versa) silently renders a dead link or drops content that was still present.

Proposal: delete FullReportOnly and let presence of the field in the measurement be the sole control. Stripped ⇒ absent ⇒ not rendered. The strip dictionary on the stage stays the single declaration of what self-contained reports carry.

Why this works today

Every current FullReportOnly site gates UI whose data is already in that stage's strip dictionary, and most sites already do the presence check — the wrapper is pure redundancy:

Site	Gated field(s)	Stripped by
src/compare/stages/shared/perf-report.tsx:191	benchReportHref, control/experimentLighthouseHref, timelineHref, diffHrefs	PerfEngineStage (src/compare/stages/perf/stage.ts:53)
src/audit/stages/audit/report.tsx:101	lighthouseHref	AuditStage (src/audit/stages/audit/stage.ts:53)
src/audit/stages/accessibility/report-preview.tsx:101	rawArtifactHref	AccessibilityStage (src/audit/stages/accessibility/stage.ts:34)
src/compare/stages/accessibility/report.tsx:550, 726	comparisonArtifactHref, control/experiment.rawArtifactHref (via RawLinks)	AccessibilityCompareStage (src/compare/stages/accessibility/stage.ts:34)
src/compare/stages/accessibility/report.tsx:1034	sideRawArtifactHref(...)	same

ArtifactLinks and RawLinks both already return null when their link list is empty; the audit/a11y sites already sit behind a href ? … : null. Dropping the wrapper changes nothing about the rendered output.

Scope

1. Remove the 6 <FullReportOnly> wrappers above, keeping/adding the plain presence check where it isn't already there.
2. src/audit/stages/build_annotated_timeline/report.tsx:39,64 — same class of thing via the hook: screencastHref={mode === 'self-contained' ? undefined : row.timeline.screencastHref}. screencastHref is already in that stage's strip (stage.ts:129), so this becomes screencastHref={row.timeline.screencastHref} and useReportMode() goes away.
3. Delete FullReportOnly from src/pipeline/report-mode.tsx. With (1)+(2) done, useReportMode / ReportModeContext / ReportModeProvider have no consumers either — delete them and drop the provider from report-shell/src/main.tsx:30. Keep the ReportMode type and meta.reportMode (used by reportDataForMode and asserted in the bisect tests) as metadata about which file this is.
4. Type check: each stripped key must be optional on its measurement interface so the presence check compiles and so applySelfContainedReportStrip removing it isn't a lie about the type. Verify for all of: lighthouseHref, lighthouseThumbHref, coverageStatementIdsHref, controlLighthouseHref, experimentLighthouseHref, timelineHref, benchReportHref, diffHrefs, rawArtifactHref, comparisonArtifactHref, screencastHref.
5. Update the review-architecture skill (.claude/skills/review-architecture/SKILL.md:186,256) so the checklist says the strip dictionary is the only control and there is no render-mode gate to keep in sync.

Risks / things to check

• reportDataForMode no-ops the strip when stages is empty (src/pipeline/report.ts:326 — shouldStrip requires selfContainedStrips.size > 0), and writeReport's stages param defaults to []. Today FullReportOnly is a backstop for that path; after this change a self-contained report built without stages would render live artifact links. Both real callers pass stages (src/pipeline/runner.ts:789, src/compare/bisect/report.ts:44), so the fix is to make stages required on writeReport (or fail loudly when it's empty) as part of this change.
• Sites that consume a stripped field outside a FullReportOnly need a look while we're in there — e.g. src/compare/stages/accessibility/report.tsx:~554 passes href={result.comparisonArtifactHref ?? '#'} to DetailedArtifactDialog, i.e. a self-contained report gets an '#' href. Not a regression from this change, but presence-based rendering is the moment to decide what that dialog should do when the artifact isn't there.
• Tests referencing the removed component / mode gate: src/pipeline/__tests__/report.test.ts, test/audit/accessibility-report-ui_spec.ts, test/compare/bisect-report-ui_spec.ts. The UI specs should keep asserting "no raw-artifact links in self-contained output" — that assertion is the real regression guard once the wrapper is gone.

Acceptance

• No FullReportOnly / useReportMode left in the tree.
• Self-contained and full report HTML byte-compare equivalent to before the change for a fixture run (same links present/absent).
• A stage can now control self-contained rendering by editing only its selfContainedReportStrip.