Fixes panic: assignment to entry in nil map in PMG polling tests.
**Problem:**
Tests were manually creating Monitor structs without initializing internal
maps like pollStatusMap, causing nil map panics when recordTaskResult()
tried to update task status.
**Root Cause:**
- TestPollPMGInstancePopulatesState (line 90)
- TestPollPMGInstanceRecordsAuthFailures (line 189)
Both created Monitor with only partial field initialization, missing:
- pollStatusMap
- dlqInsightMap
- instanceInfoCache
- Other internal state maps
**Solution:**
Changed both tests to use New() constructor which properly initializes all
maps and internal state (monitor.go:1541). This ensures tests match production
initialization and will automatically pick up any future map additions.
**Tests:**
✅ TestPollPMGInstancePopulatesState - now passes
✅ TestPollPMGInstanceRecordsAuthFailures - now passes
✅ All monitoring tests pass (0.125s)
Follows best practice: use constructors instead of manual struct creation
to maintain initialization invariants.
