feat: Modernize and open-source

[afshin]

This PR gets notebook-metrics much closer to first open-source release shape.
It renames the package surfaces from notebook_link_metrics to
notebook_metrics / notebook-metrics, cleans up release and onboarding
material, and hardens the implementation and tests around the core metrics
flows.

Highlights

• Rename Python package, config, and test surfaces to notebook_metrics /
  notebook-metrics and align install metadata, schemas, and server config.
• Add release-facing project polish: BSD licensing cleanup, new onboarding and
  release documentation, dependency modernization, and CI updates for build and
  integration coverage.
• Replace the JupyterError backend from rendermime interception to notebook
  execution failures while preserving the existing schema URL and payload shape.
• Harden dispatcher behavior by catching collector failures and continuing to
  dispatch subsequent events.
• Expand unit and integration coverage, including backend event-capture support
  and Playwright coverage for command, notebook-execution, and runtime-error
  emissions.
• Record the validated frontend runtime expectations with Node >=24 and move
  TypeScript off the deprecated moduleResolution: "node" setting.

[Copilot]

Pull request overview

This PR prepares notebook-metrics for an initial open-source release by renaming package surfaces (Python + npm), modernizing dependencies/CI, and tightening the core metrics emission/dispatch flows with expanded unit + UI test coverage.

Changes:

• Rename package identifiers from notebook_link_metrics / @notebook-link/metrics to notebook_metrics / notebook-metrics across code, config, docs, and CI.
• Rework the JupyterError metric to be emitted from notebook execution failures (via NotebookActions.executed) and harden dispatching by catching collector failures.
• Add/expand Jest + Playwright integration coverage, including a test-only server extension to capture backend events.

Reviewed changes

Copilot reviewed 32 out of 40 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
yarn.lock	Updates frontend dependency lockfile to newer JupyterLab/related packages.
ui-tests/tests/notebook_metrics.spec.ts	Adds Playwright coverage for backend-captured command, execution error, and runtime error emissions.
ui-tests/tests/notebook_link_metrics.spec.ts	Removes legacy placeholder UI test for the old package name.
ui-tests/README.md	Updates UI test instructions and recommends disabling auto-open of HTML report.
ui-tests/playwright.config.js	Improves webServer shutdown handling and adjusts stdout/stderr capture.
ui-tests/package.json	Renames UI tests package, bumps Galata/Playwright, and sets Node engine to >=24.
ui-tests/metrics-override.yml	Adds a test override to enable/allow the built-in schemas during UI tests.
ui-tests/jupyter_server_test_config.py	Configures Jupyter server for UI tests, enabling notebook_metrics + capture extension and setting override env var.
ui-tests/event_capture_extension.py	Adds a test-only server extension to capture emitted metrics via a REST API.
tsconfig.json	Switches TS moduleResolution to bundler and enables skipLibCheck.
src/plugins.ts	Updates plugin IDs/name usage, removes rendermime dependency, merges excluded config sources, and catches collector failures.
src/metrics.ts	Renames exported plugin ID constants to notebook-metrics:* and updates imports to type-only where appropriate.
src/emissions/jupyter-error.ts	Changes JupyterError emission source from rendermime interception to notebook execution failures.
src/tests/notebook_metrics.spec.ts	Adds substantial Jest coverage for emissions + dispatcher filtering/override behavior and collector failure handling.
src/tests/notebook_link_metrics.spec.ts	Removes legacy placeholder Jest test for the old package name.
schema/dispatcher.json	Updates settings schema title/description to the new project naming.
RELEASE.md	Rewrites release documentation for the new package names and Jupyter Releaser-driven flow.
README.md	Updates public docs for new naming, install/uninstall, requirements, and test workflows.
pyproject.toml	Renames PyPI project to notebook-metrics and updates build artifact paths to notebook_metrics.
package.json	Renames npm package, updates license to BSD-3-Clause, bumps JupyterLab deps, and sets Node engine to >=24.
ONBOARDING.md	Adds detailed onboarding guide covering mental model, configuration precedence, and integration paths.
notebook_metrics/tests/test_pass.py	Adds Python tests for schema registration and backend listener collection behavior.
notebook_metrics/tests/init.py	Adds test package marker/docstring for notebook_metrics tests.
notebook_metrics/emissions/runtime-error.yml	Adds runtime-error event schema YAML under new package layout.
notebook_metrics/emissions/jupyter-error.yml	Updates schema title/description to reflect notebook execution error semantics.
notebook_metrics/emissions/current-changed.yml	Adds current-changed event schema YAML under new package layout.
notebook_metrics/emissions/command-executed.yml	Adds command-executed event schema YAML under new package layout.
notebook_metrics/init.py	Updates declared JS/Python package names and keeps schema registration + override injection.
notebook_link_metrics/tests/test_pass.py	Removes obsolete test file under old Python package name.
notebook_link_metrics/tests/init.py	Removes obsolete test package marker under old Python package name.
LICENSE	Replaces “UNLICENSED” with BSD-3-Clause license text.
jupyter-config/server-config/notebook_metrics.json	Updates server extension enablement name to notebook_metrics.
jest.config.js	Updates Jest ESM transform allowlist and ignores generated labextension output under notebook_metrics.
install.json	Updates installation metadata to new PyPI project name notebook-metrics.
conftest.py	Updates pytest Jupyter server extension enablement name to notebook_metrics.
.prettierignore	Updates ignore path from notebook_link_metrics to notebook_metrics.
.gitignore	Updates ignored labextension/version paths to notebook_metrics and adds junit.xml + .vscode.
.github/workflows/build.yml	Updates CI for renamed artifacts/packages and Playwright artifact naming.
.copier-answers.yml	Updates copier metadata to new labextension/python package names.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.