[43/44] Enable TS strict mode in dotcms-binary-field-builder

Description

Part of the strict-mode rollout epic #35932.

The original acceptance criteria were stale. They described a typescript-strict-plugin /
npx tsc-strict / @ts-strict-ignore approach that was dropped early in the epic. The approach
actually in force is in core-web/CLAUDE.md → TypeScript Strict Mode:
the six flags go in the project's own tsconfig.json, and tsconfig.base.json stays
"strict": false. Rewritten below to match.

Acceptance Criteria

• The six flags are in the project's own tsconfig.json:
  forceConsistentCasingInFileNames, strict, noImplicitOverride,
  noPropertyAccessFromIndexSignature, noImplicitReturns, noFallthroughCasesInSwitch.
• tsconfig.spec.json does not override them.
• tsc -p reports 0 on both the lib/app config and the spec config.
• No new any; no production non-null assertions added.
• nx run <project>:lint and :test pass.
• Blast radius verified across the strict projects.

Priority

Medium

Additional Context

Unblocked by edit-content (#35974) reaching 0. See the evidence comment below.

Read core-web/CLAUDE.md under TypeScript Strict Mode, then inspect the dotcms-binary-field-builder project's tsconfig.json and tsconfig.spec.json. Run tsc -p for both configurations, followed by the project's Nx lint and test targets. Done means the six strict flags are project-local, both type checks report zero errors, and the stated lint, test, and blast-radius checks pass.