feat: add structured logging to the intents WebSocket gateway

[Paranoa-dev]

Add Structured Logging for WebSocket Events

Summary

This PR adds structured logging to IntentsGateway using the shared winston logger from src/common/logger.ts, providing operators with visibility into WebSocket activity that was previously silent.

Problem

The WebSocket gateway had zero logging — connects, disconnects, and broadcasts happened silently. Unlike HTTP requests (logged via LoggingInterceptor), there was no way to observe WS activity in production logs.

Changes

src/intents/intents.gateway.ts

• Imported the shared logger from src/common/logger.ts
• Connection logging: Logs ws client connected (subscribers=N) on each new connection, showing the current subscriber count
• Disconnection logging: Logs ws client disconnected (subscribers=N) on each disconnect
• Broadcast logging: Logs ws broadcast type=<eventType> subscribers=N at debug level for every broadcast — captures event type only (not payload) to avoid log volume blowup
• Heartbeat logging: Logs ws heartbeat started on gateway construction, and ws heartbeat terminated dead client (subscribers=N) when a dead client is cleaned up
• Added getSubscriberCount(): Exposes the raw subscriber count (separate from the existing getAliveCount() which only counts clients that responded to the last ping)

src/intents/intents.gateway.spec.ts

Added a new IntentsGateway logging test suite with 5 tests verifying:

• Heartbeat started is logged on construction
• Connection includes subscriber count
• Disconnection includes subscriber count
• Broadcast logs event type without payload data
• Dead client termination logs subscriber count

Log Format

All logs follow the existing winston format: ISO_TIMESTAMP [level] message

2026-07-28T10:36:18.504Z [info] ws heartbeat started
2026-07-28T10:36:19.011Z [info] ws client connected (subscribers=1)
2026-07-28T10:36:19.511Z [debug] ws broadcast type=intent_created subscribers=1
2026-07-28T10:36:20.352Z [info] ws client disconnected (subscribers=0)
2026-07-28T10:36:50.000Z [debug] ws heartbeat terminated dead client (subscribers=0)

Design Decisions

• Event type only, no payload: Broadcast logs include the event type (e.g., intent_created) but not the full payload, to prevent log volume blowup with large intent objects
• Debug level for broadcasts: Broadcast and heartbeat termination logs use debug level (only visible in non-production), while connect/disconnect use info level for production visibility
• Subscriber count included: Every log message includes the current subscriber count for context

Test Results

Unit tests:  29 passed (4 suites)
E2e tests:   23 passed (5 suites)
Total:       52 tests passing

Checklist

• Uses shared winston logger from src/common/logger.ts
• Logs connection count changes
• Logs broadcast event types (not payloads)
• Logs heartbeat lifecycle events
• Unit tests for all logging behavior
• npm run lint passes
• npm run typecheck passes
• npm test passes
• npm run test:e2e passes

Closes #82

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