feat(telemetry): opt-in anonymous learning-funnel events

[OthmaneZ05]

Summary of Changes

Adds strictly opt-in, anonymous product telemetry for the learning funnel. Five custom events (roadmap_started, step_validated, step_failed, roadmap_completed, roadmap_abandoned) are sent as Plausible-format custom events to a build-time-configurable endpoint (VITE_TELEMETRY_ENDPOINT / VITE_TELEMETRY_DOMAIN; an empty endpoint hard-disables telemetry entirely).

• Consent is tri-state (unset / accepted / declined, localStorage key torollo_telemetry_consent): anything other than an explicit accept means zero network requests. A one-time, non-blocking consent card on the home screen asks the question; a header toggle makes the choice reversible at any time.
• Anonymous by construction: payloads carry only the catalogue roadmap id, step id, app version and a random locally-generated install id. Revoking consent deletes the install id, so re-enabling starts a fresh identity. No PII, no project names, no server-side collector in this repo.
• Honest counting: step_failed only counts pedagogical failures — validator runs that end in an engine error (e.g. Docker unreachable) are not counted; roadmap_started only fires when the backend progress store is confirmed empty; roadmap_completed fires once, on the validation that completes the roadmap; roadmap_abandoned fires once per play-through on close/unmount/pagehide (with keepalive so it survives tab close).
• New README Telemetry section documents the exact event list, payload contents, and how to decline/revoke.

Types of Changes

• New feature / node type addition
• Bug fix (non-breaking change resolving an issue)
• Refactoring / structural cleanup
• Documentation update

Verification & Testing

Automated Checks

• Run npm run lint successfully with no errors
• Run npm run build successfully with no compilation errors
• Run npm test successfully (all tests pass)

322 frontend tests pass, including new suites: consent store (tri-state, install-id lifecycle, storage-disabled fallback), trackEvent (zero fetch calls when declined/unset, exact payload prop allowlist, keepalive passthrough, never throws on network failure), and the player hook wiring for all five events (including the no-restart-on-resume and no-abandon-after-completion negatives).

Manual Verification

Full E2E run against the real backend + real Docker with a local Plausible-shaped capture server and Playwright driving the UI (20/20 checks):

• Declined: played a real roadmap (open, validate against real containers, close) — zero requests on the wire, asserted from the browser's request log, not just the capture file.
• Accepted via the header toggle: all five events arrived for real — fresh open (roadmap_started), a real validator pass (step_validated), a real fail on a missing container (step_failed), closing mid-roadmap (roadmap_abandoned with the correct step id), and creating the missing container then validating (step_validated + roadmap_completed).
• Negatives: reopening with saved progress fires no second roadmap_started; closing a completed roadmap fires no roadmap_abandoned.
• Payload audit across all captured events: props limited to roadmap/step/install_id/app_version, one stable random install id, configured domain honoured, no PII strings.
• Consent card and toggle verified visually in light and dark themes.
• Production pipeline smoke-tested: a test event POSTed with the app's exact payload shape was accepted (202) by the production Plausible instance and appears in the dashboard.

Checklist

• My code follows the repository's code style and lint standards
• I have updated the documentation or instructions if necessary
• All unit and integration tests are passing

🤖 Generated with Claude Code