Add PostHog analytics integration

[posthog]

Summary

This PR adds PostHog analytics to mcplint using the posthog-node SDK (installed via npm). The setup wizard instrumented the CLI to capture events at every meaningful exit point.

• src/posthog.ts — new PostHog singleton client (Node SDK, flushAt: 1, flushInterval: 0, exception autocapture) for CLI-safe flushing
• src/cli.ts — imports the client and captures events for successful lint runs, snapshot dumps, rule explanations, threshold failures, and unhandled errors
• package.json / package-lock.json — adds posthog-node@^5.45.2
• .gitignore — ignores .env so the API key is never committed

Captured events: lint_run_completed, snapshot_dumped, rule_explained, lint_threshold_failed, lint_run_errored.

Insights and dashboards created

Type	Name	Link
Dashboard	Analytics basics (wizard)	https://us.posthog.com/project/520619/dashboard/1875473
Insight	Lint runs over time	https://us.posthog.com/project/520619/insights/MpBKFY9t
Insight	Lint runs by source	https://us.posthog.com/project/520619/insights/ODLqrmVn
Insight	Avg composite score	https://us.posthog.com/project/520619/insights/iyjP2y90
Insight	Threshold failures	https://us.posthog.com/project/520619/insights/6m9QvhnX
Insight	Rules explained	https://us.posthog.com/project/520619/insights/3uttxtHV

How to verify

1. Build and run the CLI against a fixture, with the env vars from the section below set in your shell:

   npm run build
   export POSTHOG_API_KEY=phc_nWALq8MXGHFzBUQ9JxTVQoY4VEYjZd3SXC5ZduKQMPtX
   export POSTHOG_HOST=https://us.i.posthog.com
   npm run lint:good

2. In PostHog, open Activity — you should see a lint_run_completed event arrive within a minute.
3. Confirm the dashboard populates: Analytics basics (wizard).

Environment variables (action needed before PostHog works)

mcplint is a Node CLI distributed via npm (run with npx mcplint). There is no server deployment and no committed runtime config file read in production — the code reads process.env.POSTHOG_API_KEY / POSTHOG_HOST directly, and .env is both gitignored and excluded from the npm files bundle, so it would never reach end users anyway. "Production" for a CLI is each user's own shell, so these variables must be set in the environment where the CLI runs.

Name	Value
POSTHOG_API_KEY	phc_nWALq8MXGHFzBUQ9JxTVQoY4VEYjZd3SXC5ZduKQMPtX
POSTHOG_HOST	https://us.i.posthog.com

Set them wherever you run mcplint — e.g. in your shell profile (~/.bashrc / ~/.zshrc) or your CI runner's secret store — and ensure they are exported into the process environment before invoking npx mcplint.

export POSTHOG_API_KEY=phc_nWALq8MXGHFzBUQ9JxTVQoY4VEYjZd3SXC5ZduKQMPtX
export POSTHOG_HOST=https://us.i.posthog.com

When unset, PostHog initializes with an empty key and silently no-ops — the linter still runs normally, it just does not emit analytics.

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Created with PostHog Code

[posthog]

CI status

This repository has no .github/workflows/ configured, so there are no CI checks running on this branch (gh pr checks reports "no checks reported"). Nothing to keep green — verified the build, type-check, and test suite all pass locally before opening this PR:

• npm run build ✅
• npm run typecheck ✅
• npm test ✅ (30 tests passed)

Note: package.json has no lint script, so that step was skipped (the repo genuinely doesn't define one).