[23/44] Enable TS strict mode in new-block-editor

Description

Part of the strict-mode rollout epic #35932. Enable TypeScript strict mode for the new-block-editor project.

• Internal dependents: 4 · Rollout order: 23 / 44

Note: the original acceptance criteria referenced typescript-strict-plugin, npx tsc-strict, and // @ts-strict-ignore. That approach was dropped by the epic — the plugin was never installed. The ACs below reflect the approach in force, documented in core-web/CLAUDE.md → TypeScript Strict Mode.

Acceptance Criteria

• The six strict flags are present in the project's own tsconfig.json:
  forceConsistentCasingInFileNames, strict, noImplicitOverride, noPropertyAccessFromIndexSignature, noImplicitReturns, noFallthroughCasesInSwitch.
• tsc -p <projectRoot>/tsconfig.lib.json --noEmit reports 0 errors (tsconfig.app.json for apps).
• tsc -p <projectRoot>/tsconfig.spec.json --noEmit reports 0 errors.
• All errors resolved with explicit types — no new any.
• nx run <project>:lint and :test pass, with the test count unchanged.
• nx affected -t build,lint does not break dependents.
• The enforcement status is recorded — i.e. whether any CI gate actually verifies the strictness.

⚠️ Four things established earlier in this rollout that make error counts untrustworthy:

• :test does not type-check. isolatedModules: true puts ts-jest in transpile-only mode (#35948), so passing tests say nothing about types. tsc -p is the acceptance test — but run the tests anyway, since they catch behaviour changes tsc cannot.
• A files entry pointing at a missing file (TS6053, #35947) or an uninstalled types entry (TS2688, #35944) aborts tsc before semantic checking.
• tsc does not check templates. Only a build does, and most projects here have no build target (#35970).
• Check moduleResolution. node10 cannot resolve the @dotcms/* subpath exports, which inflated dot-plugins from 63 real errors to 733 (#35966). Match dot-tags: bundler + module: "preserve".

Priority

Medium

Additional Context

One project in the bottom-up rollout tracked by epic #35932.

Start with the TypeScript Strict Mode guidance in core-web/CLAUDE.md, then inspect the new-block-editor project's own tsconfig.json, tsconfig.lib.json, and tsconfig.spec.json. Run the specified tsc checks first, resolve reported errors with explicit types, and run the Nx lint, test, and affected build/lint commands. Done means all six flags are present, checks pass with unchanged tests, dependents remain working, and enforcement status is recorded.