Bring the new skill system branch up to date with dev. Conflicts resolved
in favor of the new skill-system architecture: built-in skill .ts files
(including dev-added tracks, browser-control, composio-integration) are
deleted in favor of SKILL.md content sourced from outside the source tree.
buildCopilotInstructions now sources the catalog from SkillResolver and
filters composio-integration when Composio is not configured.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>