Address review against GitHub Copilot CLI docs (add-custom-instructions):
- COPILOT_CUSTOM_INSTRUCTIONS_DIRS: each dir contributes AGENTS.md (context) and .github/instructions/**/*.instructions.md (recursive), per spec. Dropped the non-spec <dir>/copilot-instructions.md and the wrong top-level <dir>/*.instructions.md scan.
- Scan the project .github/instructions/ tree recursively ('within or below').
- Prompts: .github/prompts/*.prompt.md is a VS Code construct, not a Copilot CLI feature; dropped the fictional ~/.copilot/prompts/ user dir and reframed comments/descriptions accordingly.
The github provider only scanned the project .github/ tree, so Copilot CLI's user-global config was ignored. Add user-global instructions (~/.copilot/copilot-instructions.md), COPILOT_HOME relocation, COPILOT_CUSTOM_INSTRUCTIONS_DIRS (copilot-instructions.md + *.instructions.md), and prompt discovery (*.prompt.md in .github/prompts/ and ~/.copilot/prompts/).
Closes#1913, #1915, #1916.
Asaf Mahlev