Got rid of forced tutorial and added auto opt in for CLI analytics

[rvvance]

• Removes forced tutorial, agent-skill, and analytics prompts; scripted use of brev no longer blocks on interactive dialogs.
• Switches analytics from opt-in to opt-out; adds brev analytics on/off and honors DO_NOT_TRACK=1 / BREV_NO_ANALYTICS=1. Explicit opt-outs are preserved across upgrade.
• New non-blocking hint points fresh users at brev hello; Quick Start now shows at the top of brev --help
• also edited the agent skill to install for codex instead of just claude

[patelspratik]

some Claude feedback that seems worth doing

• Likely orphaned hello helpers. With ls.go and cmd.go's onboarding hooks gone, hello.ShouldWeRunOnboardingLSStep, hello.Step1, possibly hello.CanWeOnboard are unreferenced. Worth a grep -r and removal here or in a follow-up.
  • No tests. The env-var override matrix for IsAnalyticsEnabled() and IsDisabledByEnv() is pure logic and worth at least one unit test given the policy stakes.
• IdentifyUser missing the remote kill gate. captureEvent checks both IsAnalyticsEnabled() and IsAnalyticsFeatureEnabled(); IdentifyUser only checks the first. If posthog remote-kill is flipped off in an incident, command events stop but Alias calls keep firing. Add the second gate (or factor a shared helper).
• TrackEvent (/api/brevent) only honors IsAnalyticsEnabled, not IsAnalyticsFeatureEnabled. That's likely intentional (different telemetry channel), but the new doc-comment on IsAnalyticsFeatureEnabled reads "remote kill switch for CLI telemetry" which implies it kills all telemetry. Either narrow the comment to "posthog only" or extend the gate to TrackEvent.

[theFong]

we drop this id here I think un-intentionally