[FEATURE] Add project/repo context label to OpenTelemetry metrics

Feature Request

Claude Code's OpenTelemetry metrics and log events don't include any label indicating which project or repository a session is working in.

Why this matters

Users who work across multiple codebases see all metrics blended together in their dashboards. There's no way to filter by project, compare cost across repos, or understand which codebase drives the most token usage.

Requested change

Add a project or repository attribute to metrics and log events, derived from the git repo name or working directory of the active session.