feat: Enrich tracking events with contextual metadata

[ckbedwell]

Description

Our tracking events capture actions but lack the surrounding context needed to draw meaningful conclusions. We should attach additional metadata properties to events describing the user's state and environment.

Use Case / Motivation

• Without contextual metadata, we can't segment or correlate user behaviour with their setup
• Learned this the hard way with Time Point Explorer feedback — we can't tell what time range, check frequency, or screen size users had when they gave feedback
• Properties that go unused can be ignored; missing properties require a code change, release, and weeks of data accumulation

Reference: Session Replay PR review comment

Proposed Solution

Audit existing tracking events and attach contextual metadata. Candidates:

Global (most events):

• Screen size / viewport
• Total check count
• Current time range
• Current page / section

Check-specific:

• Check type, frequency, probe count
• Whether alerting is enabled

Feature-specific (e.g. Time Point Explorer, feedback):

• Time range, check frequency, visible data points
• Section the user is interacting with

Favour over-logging — unused properties cost nothing, missing ones cost months.