[v1.0] telemetry abstraction (single wrapper)

[Jonathangadeaharder]

Telemetry abstraction

Goal

A single thin wrapper (src/lib/telemetry.ts) is the only place that imports a vendor SDK. Every event, error, and pageview goes through it.

Tasks

• Define tilt-app/src/lib/telemetry.ts with track, pageview, captureError, identify, reset
• No vendor SDK imported anywhere else; ESLint rule blocks direct imports of posthog-js, @sentry/*
• Default backend: PostHog (matches user's broader stack); fall back to a no-op when PUBLIC_POSTHOG_KEY is missing
• Hook into SvelteKit handle for pageviews and handleError for unhandled exceptions
• Document in README

Acceptance

rg "posthog|sentry" in source returns matches only in the telemetry wrapper file and package.json.