fix(core): detect copilot PDF input support

[rekram1-node]

Summary

• expose PDF input capability when the Copilot Models API advertises vision and application/pdf
• preserve image-only capability for vision models that do not advertise PDF input
• port the V1 fix from fix(opencode): detect Copilot PDF input support #41522 to the V2 Copilot model catalog

Testing

• bun test test/github-copilot/models.test.ts test/plugin/provider-github-copilot.test.ts from packages/core
• clean declaration build: rm -rf node_modules/.ts-dist && bun typecheck from packages/core
• targeted oxlint on the changed source and test