VFS Paging

[jtoman]

Makes the VFS tools more powerful for the agent:

1. Allows restricting grep to a subset of paths
2. Allows the agent to ask for matching lines within each file, along with the line number
3. Allows the agent to print out specific lines within a single file instead of getting the whole file

Non-scientific experiments with these news features showed a more than 2x reduction in token usage for an analyzer workflow.