Fix copilot-metrics.json to match real API shape and clarify Metrics vs Usage Metrics API

[Copilot]

The copilot-metrics.json demo file contained fictional fields (suggestion_acceptance_rate, time_saved_per_month_hours, etc.) with invalid JSON comments — nothing matching what the actual API returns. Course materials also conflated the legacy Copilot Metrics API with the new Copilot Usage Metrics API and didn't address the common question of whether chat data is included.

copilot-metrics.json

Replaced with a valid JSON sample that mirrors the real GET /orgs/{org}/copilot/metrics response shape:

[{
  "date": "2026-03-03",
  "total_active_users": 37,
  "copilot_ide_code_completions": { ... },
  "copilot_ide_chat": { "_note": "YES, chat data is included...", "total_chats": 187, ... },
  "copilot_dotcom_chat": { "_note": "GitHub.com browser chat — absent from new Usage Metrics API", ... },
  "copilot_dotcom_pull_requests": { ... }
}]

_demo_note and _note fields serve as inline teaching annotations without requiring comment syntax.

COURSE_PLAN_MAR_2026.md

• Replaced the single "Copilot Metrics API" bullet with a side-by-side breakdown of both APIs:

	Legacy Metrics API	Usage Metrics API
Endpoint	/orgs/{org}/copilot/metrics	/enterprises/{enterprise}/copilot/metrics/reports/
Status	Deprecated April 2026	GA Feb 27, 2026
Response	Inline JSON	Signed URLs → NDJSON
GitHub.com chat	✅ copilot_dotcom_chat	❌
Agent/Edit mode	❌	✅

• Updated "What's New" table: Feb 27 entry now accurately describes the Usage Metrics API (not a vague "GA" note); added April 2026 deprecation row for the legacy endpoint.
• Added a Teaching Notes entry with the explicit answer: the legacy Metrics API did return chat data (copilot_ide_chat + copilot_dotcom_chat); the new API covers IDE chat but drops GitHub.com browser chat.

README.md

Updated the segment 4 bullet to reference both APIs and the Feb 27 GA date.

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