Add setting to disable automatic "opened file" context in VS Code extension

Feature request

Add a VS Code extension setting to disable automatically sending the currently opened file as context (ide_opened_file) with each prompt.

Problem: When using Claude Code in VS Code, the most recently opened file is always sent as context, even when no files are actively open in the editor and the task is completely unrelated. This causes Claude to misinterpret ambiguous prompts by anchoring on that file.

For example, asking "can you check 1234 and see if it's still valid?" (referring to a GitHub issue) gets misinterpreted as referring to something in the most recently opened file, because Claude sees the file context and assumes relevance.

Having to toggle context off before every prompt adds friction, especially for users who frequently ask questions unrelated to what they were last editing.