Add copilot-brag-sheet plugin — continuous work tracking for Copilot CLI sessions

[vidhartbhatia]

⚠️ On hold — reassessing contribution format

We're evaluating whether to submit this as:

1. External plugin (plugins/external.json) — current approach, but copilot plugin install won't load our joinSession() extension, which could confuse users
2. Hook contribution (hooks/work-log-tracker/) — lightweight session logger that's natively installable, with a link to the full extension for richer functionality

The repo has moved to the Microsoft org: https://github.com/microsoft/copilot-brag-sheet (MIT, public, OSMP compliant).

Will update this PR once we've decided the right path. Feedback from maintainers on the preferred approach is very welcome!

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What copilot-brag-sheet does

A Copilot CLI extension that continuously tracks every AI coding session into a structured work impact log — capturing files edited, PRs created, and git actions. Say "brag" to save an accomplishment, "review my work" to see your log.

• Repository: microsoft/copilot-brag-sheet
• 107 tests, CI on 3 OSes × 3 Node versions
• Zero dependencies, MIT licensed

Install (extension-based, not plugin-based)

curl -sL https://raw.githubusercontent.com/microsoft/copilot-brag-sheet/main/install.sh | bash

[vidhartbhatia]

Closing this — after testing, copilot plugin install does not load joinSession() extensions (tools don't appear, hooks don't fire). Listing in external.json would create a broken install experience for users.

Submitting a skill instead in a separate PR — standalone useful for writing impact statements, with a link to the full extension for automatic tracking.