feat: add PostHog analytics integration

[posthog]

Summary

This PR ships the PostHog setup wizard's integration, adding product analytics via posthog-js (browser) and posthog-node (server).

• lib/posthog-server.ts - server-side PostHog client (capturePostHogEvent, getPostHogSessionId), reads NEXT_PUBLIC_POSTHOG_PROJECT_TOKEN / NEXT_PUBLIC_POSTHOG_HOST
• instrumentation-client.ts - browser PostHog client initialization
• app/global-error.tsx - global exception capture
• components/dashboard/app-shell.tsx - persisted Clerk-backed user identification at the authenticated root boundary
• app/(app)/career/actions.ts - server-side captures for career_plan_generated, achievement_created, compensation_entry_created
• app/(app)/tribes/actions.ts - server-side capture for tribe_post_created

Insights and dashboards created

Type	Name	Link
Dashboard	Analytics basics (wizard)	https://us.posthog.com/project/546189/dashboard/1972040
Insight	Career plans generated (wizard)	https://us.posthog.com/project/546189/insights/RVJIXdMY
Insight	Achievements created (wizard)	https://us.posthog.com/project/546189/insights/noPjlZMc
Insight	Compensation entries created (wizard)	https://us.posthog.com/project/546189/insights/Z15GECvk
Insight	Tribe posts created (wizard)	https://us.posthog.com/project/546189/insights/ABKJYwhT
Insight	Career engagement actions (wizard)	https://us.posthog.com/project/546189/insights/pAKQbhe5

How to verify

1. Deploy this branch (or run it locally after setting the environment variables below).
2. Sign in and click around — generate a career plan, add an achievement or compensation entry, or create a tribe post.
3. In PostHog, open Activity — you should see career_plan_generated, achievement_created, compensation_entry_created, and tribe_post_created events arriving within a minute, plus $pageview/browser events from the client SDK.
4. Open the Analytics basics (wizard) dashboard to see the trends populate.

Environment variables (action needed before PostHog works in production)

This app deploys to Netlify (netlify.toml, docs/deploy/netlify.md), which keeps environment variables in Site settings rather than in a file committed to this repo — and the project's own deploy docs say not to commit them there. So these were not set automatically:

Name	Value
NEXT_PUBLIC_POSTHOG_PROJECT_TOKEN	phc_n9HueS97MiWZazRpsiuvnnwa9z92r6QVqWnRawaBmEC4
NEXT_PUBLIC_POSTHOG_HOST	https://us.i.posthog.com

To set them via the Netlify dashboard:

1. Open the Netlify dashboard for this site and go to Site settings → Environment variables.
2. Add each row from the table above (Key = Name, Value = Value), leaving all deploy contexts checked.
3. Redeploy the site (Deploys tab → Trigger deploy) so the new variables take effect.

Or via the Netlify CLI (already used by this project per docs/deploy/netlify.md):

echo "phc_n9HueS97MiWZazRpsiuvnnwa9z92r6QVqWnRawaBmEC4" | npx netlify env:set NEXT_PUBLIC_POSTHOG_PROJECT_TOKEN --context production
echo "https://us.i.posthog.com" | npx netlify env:set NEXT_PUBLIC_POSTHOG_HOST --context production

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Created with PostHog Code

Summary by Sourcery

Integrate PostHog analytics tracking into key career and tribes server actions to capture user engagement events.

New Features:

• Track PostHog events when users generate career plans, create achievements, and add compensation entries.
• Track PostHog events when users create tribe posts, including association with their session and identity.

Enhancements:

• Attach PostHog session identifiers derived from request headers to captured events for better analytics attribution.

[sourcery-ai]

Reviewer's Guide

Adds PostHog product analytics integration across the app, wiring both server-side event capture and client-side initialization, and instrumenting key user actions with tracked events and session IDs.

Sequence diagram for server-side PostHog event capture on career actions

sequenceDiagram
  actor User
  participant Browser
  participant NextServer
  participant PostHogServerClient
  participant PostHog

  User->>Browser: submit createCompensationAction
  Browser->>NextServer: createCompensationAction(input)
  NextServer->>NextServer: requireAppUser()
  NextServer->>NextServer: compensationSchema.parse(input)
  NextServer->>NextServer: createCompensationEntry(appUser.id, values)
  NextServer->>NextServer: headers()
  NextServer->>PostHogServerClient: getPostHogSessionId(headers)
  NextServer->>PostHogServerClient: capturePostHogEvent({distinctId, event, properties, sessionId})
  PostHogServerClient->>PostHog: send event
  NextServer->>NextServer: revalidatePath("/career")
  NextServer-->>Browser: { success, data: { entryId } }

Loading

File-Level Changes

Change	Details	Files
Instrument career-related server actions to emit PostHog analytics events for key user flows.	Import PostHog server helpers and Next.js headers API into career server actions module. After generating a 30-60-90 plan, send a PostHog event with the Clerk user ID as distinctId and a derived sessionId. After creating an achievement, send a corresponding PostHog event tied to the authenticated user and current session. After creating a compensation entry, send a PostHog event including the currency property and session association.	app/(app)/career/actions.ts
Instrument tribe post creation to emit a PostHog analytics event when a new tribe post is created.	Import PostHog server helpers and Next.js headers API into tribes server actions module. After successfully creating a tribe post, send a PostHog event keyed by the Clerk user ID and current session before revalidating paths.	app/(app)/tribes/actions.ts

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[posthog]

Heads up: the check CI job fails on this PR at the `Secret scan (basic)` step, but this is pre-existing on `main` and unrelated to this PostHog integration — the same failure occurs on the latest `main` runs (e.g. run 31146703673).

The `git grep` in .github/workflows/ci.yml matches its own pattern text (`sk_test_[A-Za-z0-9]{20,}`) inside the workflow file itself, so the step always self-triggers regardless of branch content. Since this isn't caused by the PostHog changes here and fixing it would mean editing `.github/workflows/**` (out of scope for this PR), I'm leaving it as-is and flagging it here instead.

All PostHog-specific checks pass locally: `pnpm lint`, `pnpm typecheck`, `pnpm test`, and `pnpm build` (with the CI env vars) all exit 0.