feat: batch implementation for common response formatter, featured mentors, and escrow events

[SharifIbrahimDev]

This pull request introduces a batch of requested backend and smart contract features covering API response formatting, mentor promotion, and escrow events.

What's included

• Common API Response Formatter: Implemented a global interceptor and exception filter to standardize all successful and error responses in a consistent wrapper envelope with pagination support.
• Featured Mentor Flag: Added an isFeatured flag and admin endpoints to feature top mentors on the platform. Includes a public endpoint for retrieving featured mentors and a CRON job to automatically expire the featured status after 30 days.
• SessionApproved Event: Updated the Soroban SkillSyncEscrow contract to emit a SessionApproved event when a buyer approves a session and funds are released, tracking the gross amount, fee, and net to the seller.
• DisputeOpened Event: Added a dispute_session method to the Soroban SkillSyncEscrow contract that transitions the session status to Disputed and emits a DisputeOpened event including who opened the dispute and why.
• Test Suite Fixes: Resolved several pre-existing errors in the backend test suite (including missing dependencies, mocked state side-effects, and broken TS configs) so the suite now passes successfully.

Closes #495
Closes #492
Closes #547
Closes #550

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