fix(deps): integrate all pending DevHire branches

[JasonTM17]

Summary

• consolidates all 23 pre-existing remote branches into one protected integration PR
• applies compatibility fixes for Spring Boot 4 / Spring Cloud 2025.1, Testcontainers 2, Next.js 16, Node 26, and AWS provider 6
• preserves the README learning-project positioning and updates current Spring Boot references
• keeps TypeScript on 6.0.3 because the current Next.js compiler integration does not load TypeScript 7 correctly
• upgrades Jackson 2/3, Netty, Tomcat, Spring Kafka, and Commons FileUpload to patched releases after PR image scans exposed fixed HIGH/CRITICAL CVEs

Supersedes

#84, #88, #89, #90, #92, #93, #94, #95, #96, #97, #98, #99, #100, #101, #102, #103, #104, #105, #107, #109, #110, #111, #112

Local validation

• Maven reactor: 12/12 modules, mvn -B -T1 verify (re-run after security overrides)
• Frontend: typecheck, production build, 417 tests
• Property tests: 22 tests at 500 runs each
• Playwright: 31 desktop + 21 Pixel 7 scenarios
• npm audit: 0 known vulnerabilities
• Terraform: dev/staging/prod init + validate, TFLint, Trivy IaC
• Cloud: 72 policy assertions, Helm lint/template, Kustomize, Kubeconform
• Docs/API/security/repository hygiene audits: passed
• YAML and Docker Compose configuration validation: passed

Merge policy

This PR must pass the protected master required checks and the complete Docker/image-scan matrix before squash merge. Superseded PRs and their remote branches will be closed/deleted only after the merged tree is verified byte-for-byte against this integration head.