chore(cli/telemetry): clean up audited events

[pamelachia]

Summary

CLI telemetry audit cleanup from GROWTH-797. Removes one over-firing cli_upgrade_suggested site, aligns the cli_stack_started capture pattern with the rest of the codebase, and documents an early-return invariant on TrackUpgradeSuggested so future audits don't misread the SSO update flow as a double-fire.

Changes

• cli_upgrade_suggested no longer fires on the read-only vanity-subdomains check command (kept on activate, the actual gated action). User still sees the billing-URL hint.
• cli_stack_started capture simplified to _ = phtelemetry.FromContext(ctx).Capture(...), matching cmd/root.go. Service.canSend() already handles nil receivers.
• Comment on internal/sso/update/update.go PUT branch + docstring on TrackUpgradeSuggested explaining that GET-fail and PUT-fail are mutually exclusive via early-return, so at most one event fires per command invocation. Deleting one site without the other undercounts gated users.

Testing

Tested locally in apps/cli-go:

• go test ./internal/login/... ./internal/telemetry/... ./internal/start/... ./internal/sso/... ./internal/vanity_subdomains/... -count=1 — all pass.
• cli_stack_started group/event assertion at internal/start/start_test.go:248-253 still passes after the nil-guard removal.
• go vet ./... and go build ./... clean.

Post-merge verification on PostHog:

• cli_upgrade_suggested volume on feature_key = 'vanity_subdomain' should drop (was firing on both check and activate; now only activate).

Linear

• fixes GROWTH-797

[coveralls]

Coverage Report for CI Build 25746590455

Coverage decreased (-0.007%) to 63.734%

Details

• Coverage decreased (-0.007%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 17 coverage regressions across 4 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

17 previously-covered lines in 4 files lost coverage.

File	Lines Losing Coverage	Coverage
internal/start/start.go	8	64.66%
internal/utils/git.go	5	57.14%
internal/sso/update/update.go	2	51.19%
internal/storage/rm/rm.go	2	80.61%

---

Coverage Stats

Relevant Lines:	15676
Covered Lines:	9991
Line Coverage:	63.73%
Coverage Strength:	7.06 hits per line

---

💛 - Coveralls