feat(telemetry): CLI flow events - #243

What

Foundations (#238)

• Fixes the telemetry client lifecycle: Close() deferred in Execute() with a 3s timeout; NoOpTelemetryClient fallback on init failure.
• Track with custom properties + monotonic sequence counter per invocation.
• Event catalog (events.go): Flow/Step/Direction/ErrorClass enums, FlowTracker, event name constants.
• Command Completed emitted before final flush; guard against orphan events when PersistentPreRunE never ran.

Auth flow events (#239)

• RunOAuthFlow emits CLI Auth Started → one terminal event (Completed/Aborted/Failed) with step, duration_ms, error_class.
• Event struct + typed constructors + nil-safe TrackEvent(ctx, Event) helper.
• Shared telemetrytest.RecordingClient for flow event tests.

Logout flow event (#242)

• auth logout emits CLI Auth Logout (flow: logout) before ClearToken().
• No event when already signed out; no Identify at logout.

Application create + plan change flow events (#240)

• application create: CLI Application Create Started → Completed/Aborted/Failed with step, region, plan, duration_ms, reason. Dry runs not tracked.
• application upgrade/downgrade: CLI Application Plan Change * with direction, from_plan, to_plan.
• Every Aborted carries a reason (declined_terms/cancelled/billing_required/already_on_plan/no_candidates).

Env header (#241)

• Every telemetry request carries X-Algolia-CLI-Env: prod (semver build) or dev (source build). Transport clones the request.
• Fixes double slash in telemetry URL (//v1/batch).
• Remaining outside repo: create "CLI (PROD)" Segment source; route telemetry-proxy on the header.

Test

Go on the CLI Segment debugger: https://app.segment.com/algolia-app/sources/segment_cli_dev/debugger

Then try the following commands. You should see the events being logged into Segment. sequence property + timestamp combo indicate the real order of events (Segment sometimes shows events in the wrong order)

# Foundations + Command Completed
go run ./cmd/algolia application plans

# Auth flow: Started → Completed
go run ./cmd/algolia auth login

# Abort mid-flow (Esc/Ctrl-C during app selection) → Aborted {step: app_select}
go run ./cmd/algolia auth login

# Signup variant
go run ./cmd/algolia auth signup

# Logout (signed in → event emitted; already signed out → no event)
go run ./cmd/algolia auth logout

# Application create + plan change funnels
go run ./cmd/algolia application create
go run ./cmd/algolia application upgrade
go run ./cmd/algolia application downgrade

GROUT-349
GROUT-351