[feat] Add Copilot usage, sessions, and dashboard telemetry

Context

Follow-up to #549 and merged PR #601. Copilot hooks are installed, but the support matrix still leaves usage, sessions, and dashboard unimplemented because the Copilot event and usage payloads have not been validated end to end.

Scope

• Map official Copilot hook events and tool payloads into TeamAI usage and session events.
• Record skill usage, session lifecycle, tool activity, and privacy-safe aggregates.
• Determine token usage from an official supported payload or local Copilot session storage without recording prompt contents.
• Feed the existing TeamAI dashboard and reports; do not create a Copilot-only dashboard.

Acceptance criteria

• RED to GREEN tests cover event mapping, stable session IDs, skill usage, lifecycle aggregation, redaction, and missing-token fallback.
• A real authenticated Copilot CLI session produces usage, session, and dashboard records.
• No prompt text, secrets, or unrelated Copilot data are persisted.
• Full local CI and bilingual documentation are green.

This is a separate child delivery of #549 because telemetry has a distinct privacy and payload-validation contract.