[29/44] Enable TS strict mode in portlets-dot-categories-portlet

Description

Part of the strict-mode rollout epic #35932. Enable TypeScript strict mode for the portlets-dot-categories-portlet project.

• Internal dependents: 1 · Rollout order: 29 / 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.

⚠️ Three 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.
• 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 in this rollout have no build target (#35970).

Priority

Medium

Additional Context

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

Start with core-web/CLAUDE.md under “TypeScript Strict Mode” and the portlets-dot-categories-portlet project's own tsconfig.json. Run the specified tsc checks for tsconfig.lib.json and tsconfig.spec.json, then use the lint, test, and affected build commands. Done means zero type errors, unchanged test count, passing checks, working dependents, and recorded CI enforcement status.