[OP-18993] Add TypeScript tooling (1/3)

[myabc]

Ticket

https://community.openproject.org/wp/OP-18993

What are you trying to accomplish?

First of three PRs that convert this repository to strict TypeScript. This one adds the tooling and converts no source file, so the bundle is byte-identical to master.

After this PR a file opts in to type checking by being renamed from .js to .ts. .ts files are checked in strict mode; .js files stay importable and unchecked.

Unlike #109 and #110, the conversion lands in reviewable steps: tooling here, then non-plugin code, then plugins and entry files.

What approach did you choose and why?

• tsconfig.json: replaces the existing file, which was unusable (DOM lib only, no include). Strict, noEmit, allowJs without checkJs, target: ES2022 so class fields keep emitting natively, and verbatimModuleSyntax so an import is only dropped when written as import type.
• src/types.d.ts: declares window.I18n and window.OpenProject, and the string modules raw-loader produces for *.svg.
• webpack: ts-loader with transpileOnly. Bundling strips types; checking stays in npm run typecheck.
• jest: @babel/preset-typescript, configured to match tsc (onlyRemoveTypeImports, allowDeclareFields).
• eslint: typescript-eslint for .ts files. Bans any, @ts-ignore and @ts-nocheck; @ts-expect-error needs a description. Rules that would force runtime edits (prefer-const and similar) are off, because the conversion PRs change types only.
• CI: runs npm run typecheck.

Version pins, each forced by a peer: typescript@~5.9 (typescript-eslint supports <6.1, npm latest is 7.x), @babel/preset-typescript@^7 (repo is on Babel 7), @types/jest@^29 (repo is on Jest 29).

Verification

Gate	Result
npm run typecheck	pass
npm test	20 suites, 256 passed, 7 skipped (same as master)
npm run lint	pass
npm run build	pass
Bundle vs master	ckeditor.js byte-identical (cmp, sha256 fb9a98c31f92406e… on both)

Each new gate was also checked to fail when it should, using a temporary canary file: a type error fails typecheck; @ts-ignore and any fail lint; a .ts module imports and runs under jest and bundles under webpack.

AI involvement

Directed: written by Claude Code from a design agreed with @myabc, then reviewed adversarially by Codex (no findings).

[Copilot]

🟢 Approval recommended

No confirmed blocking issues remain in this tooling-only change; source conversion is deferred to subsequent PRs.

0 open findings

What changed in this PR

Adds tooling for the staged TypeScript migration of the CommonMark CKEditor build, without converting runtime source files.

Changes:

• Enables strict TypeScript checking and declares browser globals and SVG imports.
• Adds TypeScript support to webpack, Jest, and ESLint.
• Adds dependencies, documentation, and a CI typecheck step.

File	Description
webpack.config.js	Resolves and transpiles TypeScript modules.
tsconfig.json	Enables strict checking while leaving JavaScript unchecked.
src/​types.d.ts	Declares OpenProject globals and SVG modules.
README.md	Documents the typechecking workflow.
package.json	Adds tooling dependencies and typecheck command.
package-lock.json	Locks updated tooling dependencies.
jest.config.js	Enables TypeScript test transformation.
eslint.config.mjs	Adds TypeScript lint rules.
babel.config.js	Configures TypeScript transpilation for tests.
.github/​workflows/​ci.yml	Runs typechecking in CI.

🧠 Review effort: Balanced

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