docs: update challenge counts, ranges, and version references to current state

[Copilot]

Documentation was last updated when the project had ~15 challenges and ran on Spring Boot 3/Java 21. The project now has 62 challenges (0–61) and has migrated to Spring Boot 4/Java 25.

README.md

• Challenge count: 61 → 62 (challenges 0–61)
• CRE link comment: 15 → 62 challenges; OpenCRE further-reading link: 14 → 62
• "Choose Your Path" table: corrected all per-environment ranges (1-87 for cloud was clearly stale)
• Docker section: added challenge-0 and challenge-61 to description and links list
• Port note: challenges 1-59 → challenges 0-61
• K8s basic: 1-6, 8, 12-43, 48-58 → 0-6, 8, 12-43, 48-61
• K8s+Vault: 1-8, 12-58 → 0-8, 12-61
• Cloud: 1-58 → 0-61
• Fixed broken link: minikube K8s list had challenge-48 label pointing to challenge-53 URL

CONTRIBUTING.md

• Config filename typo: wrong_secrets_configuration.yaml → wrong-secrets-configuration.yaml (underscore vs hyphen)

docs/ARCHITECTURE_OVERVIEW.md

• Spring Boot 3.x → 4.x
• Java 21+ → 25
• Maven 3.8+ → 3.9+

Original prompt

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This section details on the original issue you should resolve

<issue_title>update documentaiton</issue_title>
<issue_description>With all the new challenges added, springboot 4 migration, can you please:

• update the readme
• update the contributing.md
• update any other MD or java file doc to reflect the latest changes?</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes update documentaiton #2440

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