fix(analytics): capture Web Vitals with PostHog

[posthog-eu]

Problem

• The team has no real-user page performance data. PostHog Web Analytics shows pageviews but no Web Vitals (LCP, INP, CLS, FCP).
• The posthog.init call in src/lib/analytics.ts does not set capture_performance. Thus the SDK does not send $web_vitals events.
• The PostHog Web Analytics health check reports this gap as an active issue.

Origin

• Scout: signals-scout-general
• First signal: 2026-10-11
• Inbox report: open
• Task started by: auto-start, after the report was rated P3 and ready to fix

Changes

• Turn on the posthog-js Web Vitals capture in the existing init call:

     capture_exceptions: true,
+    capture_performance: { web_vitals: true },

• The existing analytics consent gate does not change. PostHog starts only after the user accepts analytics, and demo builds still send nothing.
• The SDK loads its Web Vitals script lazily from /ingest/static/…. The existing proxy already sends static/* requests to the PostHog assets host, so no proxy change is necessary.
• The invitation-URL before_send filter also applies to $web_vitals events.

Note

The consent banner and the privacy page say "pageviews, feature usage, and browser errors" ("for example" on the privacy page). Web Vitals are page-load timings in the same consented analytics scope. This PR does not change that text. Please decide if the text must name performance measurement.

Verification

• bun run format:check, bun run lint, and bun run typecheck pass.
• bun run test:unit: 20 tests in 5 files fail. The same 20 tests also fail on main without this change. They are PDF and export tests that need the ICC and font assets (bun run setup:icc), which the sandbox does not have.
• I did not run the integration tests, the e2e tests, or the build, because they need Docker services.
• After deploy: make sure that $web_vitals events arrive in PostHog and that the Web Analytics health check resolves.

Agent context

• No team notes or open PRs touch the analytics initializer. No code comment or doc in the repository records a decision to keep Web Vitals off. A full git log -S search was not possible in the partial clone.

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Created with PostHog Desktop from this inbox report.

🤖 Generated with Claude Code

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