Pause browser collectors while the panel is hidden

[mattcosta7]

Summary

Reduce addon background overhead without adding a public collection-mode API.

• start browser collectors, DOM observation, and live-update timers when the Performance panel becomes visible
• stop that work when the panel is hidden while preserving metrics already gathered for the story
• keep React Profiler callbacks attached so mount and render history is not lost before the panel opens
• resume collection automatically when the panel reopens
• document the automatic collection lifecycle

Stack

• Depends on Pause performance work while the panel is hidden #158, Pause frame metrics while previews are hidden #157, and Scope buffered performance metrics to each story #156
• This PR completes the v1.2 correctness and overhead stack

Validation

• 60 test files / 837 tests across Chromium, Firefox, WebKit, and Node
• npm run tsc
• npm run build
• publint and Are The Types Wrong: no issues
• npm run lint -- --no-cache (one pre-existing unused suppression warning)

[Copilot]

Pull request overview

Adds low-overhead core collection while retaining deeper instrumentation through opt-in diagnostic mode.

Changes:

• Adds collection-mode configuration and mode-aware collector lifecycle.
• Disables higher-overhead pointer, style, reflow, and compositor instrumentation in core mode.
• Hides most diagnostic metrics and documents mode selection.

Show a summary per file

File	Description
.changeset/collection-modes.md	Records the patch release.
README.md	Documents collection modes.
performance-panel.tsx	Conditionally displays diagnostic metrics.
decorators/universal.ts	Selects mode and recreates cores.
core/preview-core.ts	Propagates collection mode.
core/performance-types.ts	Defines mode types and parameters.
collectors/collector-manager.ts	Selects collectors by mode.
collectors/input-collector.ts	Makes pointer sampling optional.
collectors/paint-collector.ts	Makes layer scanning optional.
collectors/__tests__/collector-manager.browser.test.ts	Tests mode-specific orchestration.
collectors/__tests__/input-collector.browser.test.ts	Tests disabled pointer tracking.
collectors/__tests__/paint-collector.browser.test.ts	Tests disabled layer scanning.
__tests__/performance-decorator-universal.browser.test.ts	Tests defaults and mode changes.

Review details

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• Files reviewed: 13/13 changed files
• Comments generated: 1
• Review effort level: Balanced

[mattcosta7]

Folded into #158 so the visibility protocol and the lifecycle it controls can be reviewed and released together. #158 now includes this PR’s browser collector, DOM observation, documentation, and test changes, plus the consolidated minor changeset.