Add platform pause state indexing and propagation to all trade validation

[Chucks1093]

Summary

Index PlatformPaused and PlatformResumed events and propagate the platform pause state to all trade validation middleware so buy, sell, stake, and swap endpoints reject requests during a pause.

Scope

• Platform pause state cached in Redis on PlatformPaused event
• Cache cleared on PlatformResumed event
• Trade validation middleware checks pause state before processing any trade
• GET /platform/status — returns pause state, timestamp, and actor
• Per-key pause state checked independently in same middleware

Acceptance Criteria

• All trade endpoints return 503 with pause message during platform pause
• Pause state cached within 5 seconds of PlatformPaused event
• Cache cleared correctly on PlatformResumed event
• Platform status endpoint returns correct state and metadata
• Per-key pause correctly blocks trades for paused keys only

ETA

12 hours

[rupesh-kumar-sah]

Hello maintainers,

I would like to implement the platform pause state indexing and trade validation propagation. For this issue, I will:

1. Pause Event Indexer: Index on-chain PlatformPaused and PlatformUnpaused events with accurate timestamps and admin caller metadata.
2. In-Memory Cache / Fast Status Lookup: Maintain an indexed cache of the global pause state with sub-millisecond query latency.
3. Trade Validation Middleware: Enforce pre-flight pause checks in all trade processing routes, returning descriptive 503 Service Unavailable / Platform Paused errors when active.
4. Automated Integration Tests: Add test scenarios verifying that trades are cleanly rejected during pause and resume seamlessly post-unpause.

Ready to start right away and submit a clean PR adhering to all repo standards!