Add privacy-safe BufferDash product events

[1337lean]

Summary

• emit privacy-safe BufferDash product events for server-backed diagnostics and browser latency/stability checks
• include only the tool slug, outcome, and duration; submitted targets and browser-local inputs are excluded
• document the analytics behavior in the repository README, privacy page, and environment example

Why

BufferDash previously received page views and navigation activity but had no product-level signal for which network tools completed successfully. This adds useful operational analytics without collecting the values users submit to diagnostic tools.

Validation

• npm run lint
• npm run typecheck
• npm test (15 tests)
• npm run build
• git diff --check