Replace deprecated .substr() with .substring() across codebase

[tyevco]

Summary

There are 54 occurrences of the deprecated .substr() method across 34 files in the codebase. While .substr() still works in all runtimes (it's in Annex B of the spec), it has been deprecated in favor of .substring() or .slice().

Pattern

All instances follow the same ID generation pattern:

Math.random().toString(36).substr(2, 9)
// should become:
Math.random().toString(36).substring(2, 11)

Affected Plugins

• browser-automation-test-recorder (20 occurrences across 14 files)
• memory-performance-profiler (3 occurrences)
• logger-devtools (2 occurrences)
• api-mock-interceptor (2 occurrences)
• feature-flag-manager (2 occurrences)
• bundle-impact-analyzer, stress-testing-devtools, security-audit-panel, graphql-devtools, render-waste-detector, router-devtools, visual-regression-monitor, error-boundary-visualizer (1 each)

Migration

.substr(start, length) → .substring(start, start + length)

Before	After
.substr(2, 9)	.substring(2, 11)
.substr(2, 6)	.substring(2, 8)
.substr(2, 10)	.substring(2, 12)
.substr(2, 16)	.substring(2, 18)
.substr(2, 32)	.substring(2, 34)
.substr(2)	.substring(2)
.substr(0, 6)	.substring(0, 6)
.substr(0, 8)	.substring(0, 8)

Priority

Low — no runtime impact, but good hygiene for modern JavaScript standards.