fix(security): O_NOFOLLOW for searchFilesTool.searchContent and glob tool binary-skip

The searchFilesTool.searchContent() and the glob tool's binary-skip
path opened files with plain os.Open() — no O_NOFOLLOW. An attacker
with write access under the search root could exploit the TOCTOU
window between the filepath.Walk check and the actual open.

Both now use os.OpenFile(path, os.O_RDONLY|syscall.O_NOFOLLOW, 0),
consistent with readFileTool, batchReadTool, and all other file tools.

Fixes H1 from security audit.

Author: molty3000

cmd/odek/file_tool.go

@@ -390,7 +390,7 @@ func (t *searchFilesTool) searchContent(args searchFilesArgs) (string, error) {
 		}
 
 		// Skip binary files — single open for check then search
-		f, err := os.Open(path)
+		f, err := os.OpenFile(path, os.O_RDONLY|syscall.O_NOFOLLOW, 0)
 		if err != nil {
 			return nil
 		}

cmd/odek/perf_tools.go

@@ -1098,7 +1098,7 @@ func (t *multiGrepTool) searchPattern(pattern, root, fileGlob string, limit int)
 			}
 		}
 
-		f, err := os.Open(path)
+		f, err := os.OpenFile(path, os.O_RDONLY|syscall.O_NOFOLLOW, 0)
 		if err != nil {
 			return nil
 		}