Telemetry: instrument startup path (activation, remote setup, CLI binary)

[EhabY]

Part of the Telemetry Phase A rollout. See the RFC in Linear: AIGOV-154.

Instruments the single call chain from extension activation through workspace readiness.

Events

• activation with result, authState, measurement durationMs. Error variant adds phase.
• remote.setup (parent) with result, measurement durationMs. Wrap in TelemetryService.trace("remote.setup", ...) so all phases share a traceId.
• remote.setup.phase per phase with phase, result, measurement durationMs. Phases: auth retrieval, workspace lookup, workspace ready, SSH config write, agent ready.
• cli.download with result, reason (missing, version_mismatch, forced), measurements durationMs, sizeBytes.
• cli.verify with result, measurement durationMs.

Sites

• src/extension.ts activation function.
• src/remote/remote.ts setup flow (wrap in telemetry.trace(...)).
• src/core/cliManager.ts download and verify paths.

Tests

• Use a TestSink injected via the service container.
• Happy path emits the expected event names in order.
• Phase events share a traceId with the parent.
• Mid-phase failure emits error on the failing phase and success on prior phases.
• cli.verify failure emits the correct error fields.

Depends on AIGOV-243, ENG-2458.