I/Q: Allow searching multiple files at once

The current search tool operates on one file only. It should be possible to specify a directory or a pattern. For files which are not tracked, this should use the file content from the FS. For tracked files, it should use the buffer content.

Otherwise, agents may fall back to using standard FS tools for multi-file/directory search, thereby getting stale results in case some files have been edited but not yet saved.

Start by locating the current single-file search tool and tracing how it reads tracked and untracked files. Define the directory or pattern behavior from the issue, then verify that tracked files use buffer content while untracked files use filesystem content; no tests or file paths are named in the issue.

Written by the indexing model from the issue text.