Add Thunder API Consumer Contract Guide for Silver

[Aravinda-HWK]

📌 Description

Create Thunder API consumer contract guide for silver document.

• Closes [TASK] Create Thunder consumer contract guide #315

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🔍 Changes Made

• Add markdown file for Thunder API consumer contract guide
• Remove Silver X Thunder document.

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✅ Checklist (Email System)

• Core services tested (SMTP, IMAP, mail storage, end-to-end delivery)
• Security & compliance verified (auth via Thunder IDP, TLS, DKIM/SPF/DMARC, spam/virus filtering)
• Configuration & deployment checked (configs generated, Docker/Compose updated)
• Reliability confirmed (error handling, logging, monitoring)
• Documentation & usage notes updated (README, deployment, API)

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🧪 Testing Instructions

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📷 Screenshots / Logs (if applicable)

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⚠️ Notes for Reviewers

[gemini-code-assist]

Code Review

This pull request introduces a new documentation file, 'Thunder-API-Consumer-Contract-Guide-for-Silver.md', which outlines the API consumer contract between the Silver and Thunder teams. The review identified several inaccuracies and inconsistencies that need to be addressed: the documentation references a sample script and application that are not currently implemented, the 'id' field for admin user creation should be marked as required rather than recommended to ensure bootstrap success, and the section numbering in the endpoint contracts does not align with the summary table.

[maneeshaxyz]

LGTM.