feat: adopt Agent Plugins 1.0 for microsoft-foundry

[qinezh]

Summary

• move the Microsoft Foundry manifest to the plugin root and target the Agent Plugins 1.0 schema
• move the Copilot canvas and its preview assets under com.github.copilot/
• update the Skylight canvas sync automation to preserve the new layout and validate the portable manifest metadata

Validation

• validated microsoft-foundry/plugin.json against https://agent-plugins.org/schemas/1.0.0/plugin.schema.json
• ran node --check on the canvas extension and sync script
• parsed the updated sync workflow as YAML
• smoke-tested the sync script against a temporary copy of the v1.0.7 canvas package

Closes #676